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Table of Contents
usb_sg_wait
usb_buffer_alloc
A Universal Serial Bus (USB) is used to connect a host, such as a PC or workstation, to a number of peripheral devices. USB uses a tree structure, with the host as the root (the system's master), hubs as interior nodes, and peripherals as leaves (and slaves). Modern PCs support several such trees of USB devices, usually one USB 2.0 tree (480 Mbit/sec each) with a few USB 1.1 trees (12 Mbit/sec each) that are used when you connect a USB 1.1 device directly to the machine's "root hub".
That master/slave asymmetry was designed-in for a number of reasons, one being ease of use. It is not physically possible to assemble (legal) USB cables incorrectly: all upstream "to the host" connectors are the rectangular type (matching the sockets on root hubs), and all downstream connectors are the squarish type (or they are built into the peripheral). Also, the host software doesn't need to deal with distributed auto-configuration since the pre-designated master node manages all that. And finally, at the electrical level, bus protocol overhead is reduced by eliminating arbitration and moving scheduling into the host software.
USB 1.0 was announced in January 1996 and was revised as USB 1.1 (with improvements in hub specification and support for interrupt-out transfers) in September 1998. USB 2.0 was released in April 2000, adding high-speed transfers and transaction-translating hubs (used for USB 1.1 and 1.0 backward compatibility).
Kernel developers added USB support to Linux early in the 2.2 kernel
series, shortly before 2.3 development forked. Updates from 2.3 were
regularly folded back into 2.2 releases, which improved reliability and
brought /sbin/hotplug support as well more drivers.
Such improvements were continued in the 2.5 kernel series, where they added
USB 2.0 support, improved performance, and made the host controller drivers
(HCDs) more consistent. They also simplified the API (to make bugs less
likely) and added internal "kerneldoc" documentation.
Linux can run inside USB devices as well as on the hosts that control the devices. But USB device drivers running inside those peripherals don't do the same things as the ones running inside hosts, so they've been given a different name: gadget drivers. This document does not cover gadget drivers.
Host-side drivers for USB devices talk to the "usbcore" APIs. There are two. One is intended for general-purpose drivers (exposed through driver frameworks), and the other is for drivers that are part of the core. Such core drivers include the hub driver (which manages trees of USB devices) and several different kinds of host controller drivers, which control individual busses.
The device model seen by USB drivers is relatively complex.
USB supports four kinds of data transfers (control, bulk, interrupt, and isochronous). Two of them (control and bulk) use bandwidth as it's available, while the other two (interrupt and isochronous) are scheduled to provide guaranteed bandwidth.
The device description model includes one or more "configurations" per device, only one of which is active at a time. Devices that are capable of high-speed operation must also support full-speed configurations, along with a way to ask about the "other speed" configurations which might be used.
Configurations have one or more "interfaces", each of which may have "alternate settings". Interfaces may be standardized by USB "Class" specifications, or may be specific to a vendor or device.
USB device drivers actually bind to interfaces, not devices. Think of them as "interface drivers", though you may not see many devices where the distinction is important. Most USB devices are simple, with only one configuration, one interface, and one alternate setting.
Interfaces have one or more "endpoints", each of which supports one type and direction of data transfer such as "bulk out" or "interrupt in". The entire configuration may have up to sixteen endpoints in each direction, allocated as needed among all the interfaces.
Data transfer on USB is packetized; each endpoint has a maximum packet size. Drivers must often be aware of conventions such as flagging the end of bulk transfers using "short" (including zero length) packets.
The Linux USB API supports synchronous calls for control and bulk messages. It also supports asynchnous calls for all kinds of data transfer, using request structures called "URBs" (USB Request Blocks).
Accordingly, the USB Core API exposed to device drivers covers quite a lot of territory. You'll probably need to consult the USB 2.0 specification, available online from www.usb.org at no cost, as well as class or device specifications.
The only host-side drivers that actually touch hardware (reading/writing registers, handling IRQs, and so on) are the HCDs. In theory, all HCDs provide the same functionality through the same API. In practice, that's becoming more true on the 2.5 kernels, but there are still differences that crop up especially with fault handling. Different controllers don't necessarily report the same aspects of failures, and recovery from faults (including software-induced ones like unlinking an URB) isn't yet fully consistent. Device driver authors should make a point of doing disconnect testing (while the device is active) with each different host controller driver, to make sure drivers don't have bugs of their own as well as to make sure they aren't relying on some HCD-specific behavior. (You will need external USB 1.1 and/or USB 2.0 hubs to perform all those tests.)
Table of Contents
In <linux/usb/ch9.h> you will find
the USB data types defined in chapter 9 of the USB specification.
These data types are used throughout USB, and in APIs including
this host side API, gadget APIs, and usbfs.
struct usb_ctrlrequest — SETUP data for a USB device control request
struct usb_ctrlrequest {
__u8 bRequestType;
__u8 bRequest;
__le16 wValue;
__le16 wIndex;
__le16 wLength;
}; matches the USB bmRequestType field
matches the USB bRequest field
matches the USB wValue field (le16 byte order)
matches the USB wIndex field (le16 byte order)
matches the USB wLength field (le16 byte order)
This structure is used to send control requests to a USB device. It matches the different fields of the USB 2.0 Spec section 9.3, table 9-2. See the USB spec for a fuller description of the different fields, and what they are used for.
Note that the driver for any interface can issue control requests. For most devices, interfaces don't coordinate with each other, so such requests may be made at any time.
usb_endpoint_num — get the endpoint's number
int usb_endpoint_num ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_type — get the endpoint's transfer type
int usb_endpoint_type ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_dir_in — check if the endpoint has IN direction
int usb_endpoint_dir_in ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_dir_out — check if the endpoint has OUT direction
int usb_endpoint_dir_out ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_xfer_bulk — check if the endpoint has bulk transfer type
int usb_endpoint_xfer_bulk ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_xfer_control — check if the endpoint has control transfer type
int usb_endpoint_xfer_control ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_xfer_int — check if the endpoint has interrupt transfer type
int usb_endpoint_xfer_int ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_xfer_isoc — check if the endpoint has isochronous transfer type
int usb_endpoint_xfer_isoc ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_is_bulk_in — check if the endpoint is bulk IN
int usb_endpoint_is_bulk_in ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_is_bulk_out — check if the endpoint is bulk OUT
int usb_endpoint_is_bulk_out ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_is_int_in — check if the endpoint is interrupt IN
int usb_endpoint_is_int_in ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_is_int_out — check if the endpoint is interrupt OUT
int usb_endpoint_is_int_out ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
usb_endpoint_is_isoc_in — check if the endpoint is isochronous IN
int usb_endpoint_is_isoc_in ( | epd); |
const struct usb_endpoint_descriptor * | epd; |
Table of Contents
The host side API exposes several layers to drivers, some of which are more necessary than others. These support lifecycle models for host side drivers and devices, and support passing buffers through usbcore to some HCD that performs the I/O for the device driver.
struct usb_host_ss_ep_comp — Valid for SuperSpeed devices only
struct usb_host_ss_ep_comp {
struct usb_ss_ep_comp_descriptor desc;
unsigned char * extra;
int extralen;
}; struct usb_host_endpoint — host-side endpoint descriptor and queue
struct usb_host_endpoint {
struct usb_endpoint_descriptor desc;
struct list_head urb_list;
void * hcpriv;
struct ep_device * ep_dev;
struct usb_host_ss_ep_comp * ss_ep_comp;
unsigned char * extra;
int extralen;
int enabled;
}; descriptor for this endpoint, wMaxPacketSize in native byteorder
urbs queued to this endpoint; maintained by usbcore
for use by HCD; typically holds hardware dma queue head (QH) with one or more transfer descriptors (TDs) per urb
ep_device for sysfs info
companion descriptor information for this endpoint
descriptors following this endpoint in the configuration
how many bytes of “extra” are valid
URBs may be submitted to this endpoint
struct usb_interface — what usb device drivers talk to
struct usb_interface {
struct usb_host_interface * altsetting;
struct usb_host_interface * cur_altsetting;
unsigned num_altsetting;
struct usb_interface_assoc_descriptor * intf_assoc;
int minor;
enum usb_interface_condition condition;
unsigned is_active:1;
unsigned sysfs_files_created:1;
unsigned ep_devs_created:1;
unsigned unregistering:1;
unsigned needs_remote_wakeup:1;
unsigned needs_altsetting0:1;
unsigned needs_binding:1;
unsigned reset_running:1;
struct device dev;
struct device * usb_dev;
atomic_t pm_usage_cnt;
struct work_struct reset_ws;
}; array of interface structures, one for each alternate setting that may be selected. Each one includes a set of endpoint configurations. They will be in no particular order.
the current altsetting.
number of altsettings defined.
interface association descriptor
the minor number assigned to this interface, if this
interface is bound to a driver that uses the USB major number.
If this interface does not use the USB major, this field should
be unused. The driver should set this value in the probe
function of the driver, after it has been assigned a minor
number from the USB core by calling usb_register_dev.
binding state of the interface: not bound, binding
(in probe), bound to a driver, or unbinding (in disconnect)
flag set when the interface is bound and not suspended.
sysfs attributes exist
endpoint child pseudo-devices exist
flag set when the interface is being unregistered
flag set when the driver requires remote-wakeup capability during autosuspend.
flag set when a set-interface request for altsetting 0 has been deferred.
flag set when the driver should be re-probed or unbound following a reset or suspend operation it doesn't support.
set to 1 if the interface is currently running a
queued reset so that usb_cancel_queued_reset doesn't try to
remove from the workqueue when running inside the worker
thread. See __usb_queue_reset_device.
driver model's view of this device
if an interface is bound to the USB major, this will point to the sysfs representation for that device.
PM usage counter for this interface; autosuspend is not allowed unless the counter is 0.
Used for scheduling resets from atomic context.
USB device drivers attach to interfaces on a physical device. Each interface encapsulates a single high level function, such as feeding an audio stream to a speaker or reporting a change in a volume control. Many USB devices only have one interface. The protocol used to talk to an interface's endpoints can be defined in a usb “class” specification, or by a product's vendor. The (default) control endpoint is part of every interface, but is never listed among the interface's descriptors.
The driver that is bound to the interface can use standard driver model
calls such as dev_get_drvdata on the dev member of this structure.
Each interface may have alternate settings. The initial configuration
of a device sets altsetting 0, but the device driver can change
that setting using usb_set_interface. Alternate settings are often
used to control the use of periodic endpoints, such as by having
different endpoints use different amounts of reserved USB bandwidth.
All standards-conformant USB devices that use isochronous endpoints
will use them in non-default settings.
The USB specification says that alternate setting numbers must run from
0 to one less than the total number of alternate settings. But some
devices manage to mess this up, and the structures aren't necessarily
stored in numerical order anyhow. Use usb_altnum_to_altsetting to
look up an alternate setting in the altsetting array based on its number.
struct usb_interface_cache — long-term representation of a device interface
struct usb_interface_cache {
unsigned num_altsetting;
struct kref ref;
struct usb_host_interface altsetting[0];
}; number of altsettings defined.
reference counter.
variable-length array of interface structures, one for each alternate setting that may be selected. Each one includes a set of endpoint configurations. They will be in no particular order.
These structures persist for the lifetime of a usb_device, unlike struct usb_interface (which persists only as long as its configuration is installed). The altsetting arrays can be accessed through these structures at any time, permitting comparison of configurations and providing support for the /proc/bus/usb/devices pseudo-file.
struct usb_host_config — representation of a device's configuration
struct usb_host_config {
struct usb_config_descriptor desc;
char * string;
struct usb_interface_assoc_descriptor * intf_assoc[USB_MAXIADS];
struct usb_interface * interface[USB_MAXINTERFACES];
struct usb_interface_cache * intf_cache[USB_MAXINTERFACES];
unsigned char * extra;
int extralen;
}; the device's configuration descriptor.
pointer to the cached version of the iConfiguration string, if present for this configuration.
list of any interface association descriptors in this config
array of pointers to usb_interface structures, one for each interface in the configuration. The number of interfaces is stored in desc.bNumInterfaces. These pointers are valid only while the the configuration is active.
array of pointers to usb_interface_cache structures, one for each interface in the configuration. These structures exist for the entire life of the device.
pointer to buffer containing all extra descriptors associated with this configuration (those preceding the first interface descriptor).
length of the extra descriptors buffer.
USB devices may have multiple configurations, but only one can be active at any time. Each encapsulates a different operational environment; for example, a dual-speed device would have separate configurations for full-speed and high-speed operation. The number of configurations available is stored in the device descriptor as bNumConfigurations.
A configuration can contain multiple interfaces. Each corresponds to
a different function of the USB device, and all are available whenever
the configuration is active. The USB standard says that interfaces
are supposed to be numbered from 0 to desc.bNumInterfaces-1, but a lot
of devices get this wrong. In addition, the interface array is not
guaranteed to be sorted in numerical order. Use usb_ifnum_to_if to
look up an interface entry based on its number.
Device drivers should not attempt to activate configurations. The choice
of which configuration to install is a policy decision based on such
considerations as available power, functionality provided, and the user's
desires (expressed through userspace tools). However, drivers can call
usb_reset_configuration to reinitialize the current configuration and
all its interfaces.
struct usb_device — kernel's representation of a USB device
struct usb_device {
int devnum;
char devpath[16];
u32 route;
enum usb_device_state state;
enum usb_device_speed speed;
struct usb_tt * tt;
int ttport;
unsigned int toggle[2];
struct usb_device * parent;
struct usb_bus * bus;
struct usb_host_endpoint ep0;
struct device dev;
struct usb_device_descriptor descriptor;
struct usb_host_config * config;
struct usb_host_config * actconfig;
struct usb_host_endpoint * ep_in[16];
struct usb_host_endpoint * ep_out[16];
char ** rawdescriptors;
unsigned short bus_mA;
u8 portnum;
u8 level;
unsigned can_submit:1;
unsigned discon_suspended:1;
unsigned persist_enabled:1;
unsigned have_langid:1;
unsigned authorized:1;
unsigned authenticated:1;
unsigned wusb:1;
int string_langid;
char * product;
char * manufacturer;
char * serial;
struct list_head filelist;
#ifdef CONFIG_USB_DEVICE_CLASS
struct device * usb_classdev;
#endif
#ifdef CONFIG_USB_DEVICEFS
struct dentry * usbfs_dentry;
#endif
int maxchild;
struct usb_device * children[USB_MAXCHILDREN];
int pm_usage_cnt;
u32 quirks;
atomic_t urbnum;
unsigned long active_duration;
#ifdef CONFIG_PM
struct delayed_work autosuspend;
struct work_struct autoresume;
struct mutex pm_mutex;
unsigned long last_busy;
int autosuspend_delay;
unsigned long connect_time;
unsigned auto_pm:1;
unsigned do_remote_wakeup:1;
unsigned reset_resume:1;
unsigned autosuspend_disabled:1;
unsigned autoresume_disabled:1;
unsigned skip_sys_resume:1;
#endif
struct wusb_dev * wusb_dev;
int slot_id;
}; device number; address on a USB bus
device ID string for use in messages (e.g., /port/...)
tree topology hex string for use with xHCI
device state: configured, not attached, etc.
device speed: high/full/low (or error)
Transaction Translator info; used with low/full speed dev, highspeed hub
device port on that tt hub
one bit for each endpoint, with ([0] = IN, [1] = OUT) endpoints
our hub, unless we're the root
bus we're part of
endpoint 0 data (default control pipe)
generic device interface
USB device descriptor
all of the device's configs
the active configuration
array of IN endpoints
array of OUT endpoints
raw descriptors for each config
Current available from the bus
parent port number (origin 1)
number of USB hub ancestors
URBs may be submitted
disconnected while suspended
USB_PERSIST enabled for this device
whether string_langid is valid
policy has said we can use it; (user space) policy determines if we authorize this device to be used or not. By default, wired USB devices are authorized. WUSB devices are not, until we authorize them from user space. FIXME -- complete doc
Crypto authentication passed
device is Wireless USB
language ID for strings
iProduct string, if present (static)
iManufacturer string, if present (static)
iSerialNumber string, if present (static)
usbfs files that are open to this device
USB class device that was created for usbfs device access from userspace
usbfs dentry entry for the device
number of ports if hub
child devices - USB devices that are attached to this hub
usage counter for autosuspend
quirks of the whole device
number of URBs submitted for the whole device
total time device is not suspended
for delayed autosuspends
for autoresumes requested while in_interrupt
protects PM operations
time of last use
in jiffies
time device was first connected
autosuspend/resume in progress
remote wakeup should be enabled
needs reset instead of resume
autosuspend disabled by the user
autoresume disabled by the user
skip the next system resume
if this is a Wireless USB device, link to the WUSB specific data for the device.
Slot ID assigned by xHCI
usb_interface_claimed — returns true iff an interface is claimed
int usb_interface_claimed ( | iface); |
struct usb_interface * | iface; |
usb_make_path — returns stable device path in the usb tree
int usb_make_path ( | dev, | |
| buf, | ||
size); |
struct usb_device * | dev; |
char * | buf; |
size_t | size; |
devthe device whose path is being constructed
bufwhere to put the string
sizehow big is “buf”?
Returns length of the string (> 0) or negative if size was too small.
This identifier is intended to be “stable”, reflecting physical paths in hardware such as physical bus addresses for host controllers or ports on USB hubs. That makes it stay the same until systems are physically reconfigured, by re-cabling a tree of USB devices or by moving USB host controllers. Adding and removing devices, including virtual root hubs in host controller driver modules, does not change these path identifers; neither does rebooting or re-enumerating. These are more useful identifiers than changeable (“unstable”) ones like bus numbers or device addresses.
With a partial exception for devices connected to USB 2.0 root hubs, these identifiers are also predictable. So long as the device tree isn't changed, plugging any USB device into a given hub port always gives it the same path. Because of the use of “companion” controllers, devices connected to ports on USB 2.0 root hubs (EHCI host controllers) will get one path ID if they are high speed, and a different one if they are full or low speed.
USB_DEVICE — macro used to describe a specific usb device
USB_DEVICE ( | vend, | |
prod); |
| vend; |
| prod; |
USB_DEVICE_VER — describe a specific usb device with a version range
USB_DEVICE_VER ( | vend, | |
| prod, | ||
| lo, | ||
hi); |
| vend; |
| prod; |
| lo; |
| hi; |
USB_DEVICE_INTERFACE_PROTOCOL — describe a usb device with a specific interface protocol
USB_DEVICE_INTERFACE_PROTOCOL ( | vend, | |
| prod, | ||
pr); |
| vend; |
| prod; |
| pr; |
USB_DEVICE_INFO — macro used to describe a class of usb devices
USB_DEVICE_INFO ( | cl, | |
| sc, | ||
pr); |
| cl; |
| sc; |
| pr; |
USB_INTERFACE_INFO — macro used to describe a class of usb interfaces
USB_INTERFACE_INFO ( | cl, | |
| sc, | ||
pr); |
| cl; |
| sc; |
| pr; |
USB_DEVICE_AND_INTERFACE_INFO — describe a specific usb device with a class of usb interfaces
USB_DEVICE_AND_INTERFACE_INFO ( | vend, | |
| prod, | ||
| cl, | ||
| sc, | ||
pr); |
| vend; |
| prod; |
| cl; |
| sc; |
| pr; |
struct usbdrv_wrap — wrapper for driver-model structure
struct usbdrv_wrap {
struct device_driver driver;
int for_devices;
}; struct usb_driver — identifies USB interface driver to usbcore
struct usb_driver {
const char * name;
int (* probe) (struct usb_interface *intf,const struct usb_device_id *id);
void (* disconnect) (struct usb_interface *intf);
int (* ioctl) (struct usb_interface *intf, unsigned int code,void *buf);
int (* suspend) (struct usb_interface *intf, pm_message_t message);
int (* resume) (struct usb_interface *intf);
int (* reset_resume) (struct usb_interface *intf);
int (* pre_reset) (struct usb_interface *intf);
int (* post_reset) (struct usb_interface *intf);
const struct usb_device_id * id_table;
struct usb_dynids dynids;
struct usbdrv_wrap drvwrap;
unsigned int no_dynamic_id:1;
unsigned int supports_autosuspend:1;
unsigned int soft_unbind:1;
}; The driver name should be unique among USB drivers, and should normally be the same as the module name.
Called to see if the driver is willing to manage a particular
interface on a device. If it is, probe returns zero and uses
usb_set_intfdata to associate driver-specific data with the
interface. It may also use usb_set_interface to specify the
appropriate altsetting. If unwilling to manage the interface,
return -ENODEV, if genuine IO errors occured, an appropriate
negative errno value.
Called when the interface is no longer accessible, usually because its device has been (or is being) disconnected or the driver module is being unloaded.
Used for drivers that want to talk to userspace through the “usbfs” filesystem. This lets devices provide ways to expose information to user space regardless of where they do (or don't) show up otherwise in the filesystem.
Called when the device is going to be suspended by the system.
Called when the device is being resumed by the system.
Called when the suspended device has been reset instead of being resumed.
Called by usb_reset_device when the device
is about to be reset.
Called by usb_reset_device after the device
has been reset
USB drivers use ID table to support hotplugging. Export this with MODULE_DEVICE_TABLE(usb,...). This must be set or your driver's probe function will never get called.
used internally to hold the list of dynamically added device ids for this driver.
Driver-model core structure wrapper.
if set to 1, the USB core will not allow dynamic ids to be added to this driver by preventing the sysfs file from being created.
if set to 0, the USB core will not allow autosuspend for interfaces bound to this driver.
if set to 1, the USB core will not kill URBs and disable endpoints before calling the driver's disconnect method.
USB interface drivers must provide a name, probe and disconnect
methods, and an id_table. Other driver fields are optional.
The id_table is used in hotplugging. It holds a set of descriptors, and specialized data may be associated with each entry. That table is used by both user and kernel mode hotplugging support.
The probe and disconnect methods are called in a context where
they can sleep, but they should avoid abusing the privilege. Most
work to connect to a device should be done when the device is opened,
and undone at the last close. The disconnect code needs to address
concurrency issues with respect to open and close methods, as
well as forcing all pending I/O requests to complete (by unlinking
them as necessary, and blocking until the unlinks complete).
struct usb_device_driver — identifies USB device driver to usbcore
struct usb_device_driver {
const char * name;
int (* probe) (struct usb_device *udev);
void (* disconnect) (struct usb_device *udev);
int (* suspend) (struct usb_device *udev, pm_message_t message);
int (* resume) (struct usb_device *udev, pm_message_t message);
struct usbdrv_wrap drvwrap;
unsigned int supports_autosuspend:1;
}; The driver name should be unique among USB drivers, and should normally be the same as the module name.
Called to see if the driver is willing to manage a particular
device. If it is, probe returns zero and uses dev_set_drvdata
to associate driver-specific data with the device. If unwilling
to manage the device, return a negative errno value.
Called when the device is no longer accessible, usually because it has been (or is being) disconnected or the driver's module is being unloaded.
Called when the device is going to be suspended by the system.
Called when the device is being resumed by the system.
Driver-model core structure wrapper.
if set to 0, the USB core will not allow autosuspend for devices bound to this driver.
struct usb_class_driver — identifies a USB driver that wants to use the USB major number
struct usb_class_driver {
char * name;
char *(* devnode) (struct device *dev, mode_t *mode);
const struct file_operations * fops;
int minor_base;
}; struct urb — USB Request Block
struct urb {
struct list_head urb_list;
struct list_head anchor_list;
struct usb_anchor * anchor;
struct usb_device * dev;
struct usb_host_endpoint * ep;
unsigned int pipe;
int status;
unsigned int transfer_flags;
void * transfer_buffer;
dma_addr_t transfer_dma;
struct usb_sg_request * sg;
int num_sgs;
u32 transfer_buffer_length;
u32 actual_length;
unsigned char * setup_packet;
dma_addr_t setup_dma;
int start_frame;
int number_of_packets;
int interval;
int error_count;
void * context;
usb_complete_t complete;
struct usb_iso_packet_descriptor iso_frame_desc[0];
}; For use by current owner of the URB.
membership in the list of an anchor
to anchor URBs to a common mooring
Identifies the USB device to perform the request.
Points to the endpoint's data structure. Will eventually
replace pipe.
Holds endpoint number, direction, type, and more.
Create these values with the eight macros available;
usb_{snd,rcv}TYPEpipe(dev,endpoint), where the TYPE is “ctrl”
(control), “bulk”, “int” (interrupt), or “iso” (isochronous).
For example usb_sndbulkpipe or usb_rcvintpipe. Endpoint
numbers range from zero to fifteen. Note that “in” endpoint two
is a different endpoint (and pipe) from “out” endpoint two.
The current configuration controls the existence, type, and
maximum packet size of any given endpoint.
This is read in non-iso completion functions to get the status of the particular request. ISO requests only use it to tell whether the URB was unlinked; detailed status for each frame is in the fields of the iso_frame-desc.
A variety of flags may be used to affect how URB submission, unlinking, or operation are handled. Different kinds of URB can use different flags.
This identifies the buffer to (or from) which the I/O
request will be performed unless URB_NO_TRANSFER_DMA_MAP is set
(however, do not leave garbage in transfer_buffer even then).
This buffer must be suitable for DMA; allocate it with
kmalloc or equivalent. For transfers to “in” endpoints, contents
of this buffer will be modified. This buffer is used for the data
stage of control transfers.
When transfer_flags includes URB_NO_TRANSFER_DMA_MAP, the device driver is saying that it provided this DMA address, which the host controller driver should use in preference to the transfer_buffer.
scatter gather buffer list
number of entries in the sg list
How big is transfer_buffer. The transfer may be broken up into chunks according to the current maximum packet size for the endpoint, which is a function of the configuration and is encoded in the pipe. When the length is zero, neither transfer_buffer nor transfer_dma is used.
This is read in non-iso completion functions, and it tells how many bytes (out of transfer_buffer_length) were transferred. It will normally be the same as requested, unless either an error was reported or a short read was performed. The URB_SHORT_NOT_OK transfer flag may be used to make such short reads be reported as errors.
Only used for control transfers, this points to eight bytes of setup data. Control transfers always start by sending this data to the device. Then transfer_buffer is read or written, if needed.
For control transfers with URB_NO_SETUP_DMA_MAP set, the device driver has provided this DMA address for the setup packet. The host controller driver should use this in preference to setup_packet, but the HCD may chose to ignore the address if it must copy the setup packet into internal structures. Therefore, setup_packet must always point to a valid buffer.
Returns the initial frame for isochronous transfers.
Lists the number of ISO transfer buffers.
Specifies the polling interval for interrupt or isochronous transfers. The units are frames (milliseconds) for full and low speed devices, and microframes (1/8 millisecond) for highspeed ones.
Returns the number of ISO transfers that reported errors.
For use in completion functions. This normally points to request-specific driver context.
Completion handler. This URB is passed as the parameter to the completion function. The completion function may then do what it likes with the URB, including resubmitting or freeing it.
Used to provide arrays of ISO transfer buffers and to collect the transfer status for each buffer.
This structure identifies USB transfer requests. URBs must be allocated by
calling usb_alloc_urb and freed with a call to usb_free_urb.
Initialization may be done using various usb_fill_*_urb functions. URBs
are submitted using usb_submit_urb, and pending requests may be canceled
using usb_unlink_urb or usb_kill_urb.
Normally drivers provide I/O buffers allocated with kmalloc or otherwise
taken from the general page pool. That is provided by transfer_buffer
(control requests also use setup_packet), and host controller drivers
perform a dma mapping (and unmapping) for each buffer transferred. Those
mapping operations can be expensive on some platforms (perhaps using a dma
bounce buffer or talking to an IOMMU),
although they're cheap on commodity x86 and ppc hardware.
Alternatively, drivers may pass the URB_NO_xxx_DMA_MAP transfer flags,
which tell the host controller driver that no such mapping is needed since
the device driver is DMA-aware. For example, a device driver might
allocate a DMA buffer with usb_buffer_alloc or call usb_buffer_map.
When these transfer flags are provided, host controller drivers will
attempt to use the dma addresses found in the transfer_dma and/or
setup_dma fields rather than determining a dma address themselves.
Note that transfer_buffer must still be set if the controller does not support DMA (as indicated by bus.uses_dma) and when talking to root hub. If you have to trasfer between highmem zone and the device on such controller, create a bounce buffer or bail out with an error. If transfer_buffer cannot be set (is in highmem) and the controller is DMA capable, assign NULL to it, so that usbmon knows not to use the value. The setup_packet must always be set, so it cannot be located in highmem.
All URBs submitted must initialize the dev, pipe, transfer_flags (may be zero), and complete fields. All URBs must also initialize transfer_buffer and transfer_buffer_length. They may provide the URB_SHORT_NOT_OK transfer flag, indicating that short reads are to be treated as errors; that flag is invalid for write requests.
Bulk URBs may use the URB_ZERO_PACKET transfer flag, indicating that bulk OUT transfers should always terminate with a short packet, even if it means adding an extra zero length packet.
Control URBs must provide a setup_packet. The setup_packet and transfer_buffer may each be mapped for DMA or not, independently of the other. The transfer_flags bits URB_NO_TRANSFER_DMA_MAP and URB_NO_SETUP_DMA_MAP indicate which buffers have already been mapped. URB_NO_SETUP_DMA_MAP is ignored for non-control URBs.
Interrupt URBs must provide an interval, saying how often (in milliseconds or, for highspeed devices, 125 microsecond units) to poll for transfers. After the URB has been submitted, the interval field reflects how the transfer was actually scheduled. The polling interval may be more frequent than requested. For example, some controllers have a maximum interval of 32 milliseconds, while others support intervals of up to 1024 milliseconds. Isochronous URBs also have transfer intervals. (Note that for isochronous endpoints, as well as high speed interrupt endpoints, the encoding of the transfer interval in the endpoint descriptor is logarithmic. Device drivers must convert that value to linear units themselves.)
Isochronous URBs normally use the URB_ISO_ASAP transfer flag, telling the host controller to schedule the transfer as soon as bandwidth utilization allows, and then set start_frame to reflect the actual frame selected during submission. Otherwise drivers must specify the start_frame and handle the case where the transfer can't begin then. However, drivers won't know how bandwidth is currently allocated, and while they can find the current frame using usb_get_current_frame_number () they can't know the range for that frame number. (Ranges for frame counter values are HC-specific, and can go from 256 to 65536 frames from “now”.)
Isochronous URBs have a different data transfer model, in part because the quality of service is only “best effort”. Callers provide specially allocated URBs, with number_of_packets worth of iso_frame_desc structures at the end. Each such packet is an individual ISO transfer. Isochronous URBs are normally queued, submitted by drivers to arrange that transfers are at least double buffered, and then explicitly resubmitted in completion handlers, so that data (such as audio or video) streams at as constant a rate as the host controller scheduler can support.
The completion callback is made in_interrupt, and one of the first
things that a completion handler should do is check the status field.
The status field is provided for all URBs. It is used to report
unlinked URBs, and status for all non-ISO transfers. It should not
be examined before the URB is returned to the completion handler.
The context field is normally used to link URBs back to the relevant driver or request state.
When the completion callback is invoked for non-isochronous URBs, the actual_length field tells how many bytes were transferred. This field is updated even when the URB terminated with an error or was unlinked.
ISO transfer status is reported in the status and actual_length fields of the iso_frame_desc array, and the number of errors is reported in error_count. Completion callbacks for ISO transfers will normally (re)submit URBs to ensure a constant transfer rate.
Note that even fields marked “public” should not be touched by the driver
when the urb is owned by the hcd, that is, since the call to
usb_submit_urb till the entry into the completion routine.
usb_fill_control_urb — initializes a control urb
void usb_fill_control_urb ( | urb, | |
| dev, | ||
| pipe, | ||
| setup_packet, | ||
| transfer_buffer, | ||
| buffer_length, | ||
| complete_fn, | ||
context); |
struct urb * | urb; |
struct usb_device * | dev; |
unsigned int | pipe; |
unsigned char * | setup_packet; |
void * | transfer_buffer; |
int | buffer_length; |
usb_complete_t | complete_fn; |
void * | context; |
urbpointer to the urb to initialize.
devpointer to the struct usb_device for this urb.
pipethe endpoint pipe
setup_packetpointer to the setup_packet buffer
transfer_bufferpointer to the transfer buffer
buffer_lengthlength of the transfer buffer
complete_fnpointer to the usb_complete_t function
contextwhat to set the urb context to.
usb_fill_bulk_urb — macro to help initialize a bulk urb
void usb_fill_bulk_urb ( | urb, | |
| dev, | ||
| pipe, | ||
| transfer_buffer, | ||
| buffer_length, | ||
| complete_fn, | ||
context); |
struct urb * | urb; |
struct usb_device * | dev; |
unsigned int | pipe; |
void * | transfer_buffer; |
int | buffer_length; |
usb_complete_t | complete_fn; |
void * | context; |
urbpointer to the urb to initialize.
devpointer to the struct usb_device for this urb.
pipethe endpoint pipe
transfer_bufferpointer to the transfer buffer
buffer_lengthlength of the transfer buffer
complete_fnpointer to the usb_complete_t function
contextwhat to set the urb context to.
usb_fill_int_urb — macro to help initialize a interrupt urb
void usb_fill_int_urb ( | urb, | |
| dev, | ||
| pipe, | ||
| transfer_buffer, | ||
| buffer_length, | ||
| complete_fn, | ||
| context, | ||
interval); |
struct urb * | urb; |
struct usb_device * | dev; |
unsigned int | pipe; |
void * | transfer_buffer; |
int | buffer_length; |
usb_complete_t | complete_fn; |
void * | context; |
int | interval; |
urbpointer to the urb to initialize.
devpointer to the struct usb_device for this urb.
pipethe endpoint pipe
transfer_bufferpointer to the transfer buffer
buffer_lengthlength of the transfer buffer
complete_fnpointer to the usb_complete_t function
contextwhat to set the urb context to.
intervalwhat to set the urb interval to, encoded like the endpoint descriptor's bInterval value.
Initializes a interrupt urb with the proper information needed to submit it to a device. Note that high speed interrupt endpoints use a logarithmic encoding of the endpoint interval, and express polling intervals in microframes (eight per millisecond) rather than in frames (one per millisecond).
usb_urb_dir_in — check if an URB describes an IN transfer
int usb_urb_dir_in ( | urb); |
struct urb * | urb; |
usb_urb_dir_out — check if an URB describes an OUT transfer
int usb_urb_dir_out ( | urb); |
struct urb * | urb; |
struct usb_sg_request — support for scatter/gather I/O
struct usb_sg_request {
int status;
size_t bytes;
};
These requests are initialized using usb_sg_init, and then are used
as request handles passed to usb_sg_wait or usb_sg_cancel. Most
members of the request object aren't for driver access.
The status and bytecount values are valid only after usb_sg_wait
returns. If the status is zero, then the bytecount matches the total
from the request.
After an error completion, drivers may need to clear a halt condition on the endpoint.
Table of Contents
usb_sg_wait
usb_buffer_alloc
There are two basic I/O models in the USB API. The most elemental one is asynchronous: drivers submit requests in the form of an URB, and the URB's completion callback handle the next step. All USB transfer types support that model, although there are special cases for control URBs (which always have setup and status stages, but may not have a data stage) and isochronous URBs (which allow large packets and include per-packet fault reports). Built on top of that is synchronous API support, where a driver calls a routine that allocates one or more URBs, submits them, and waits until they complete. There are synchronous wrappers for single-buffer control and bulk transfers (which are awkward to use in some driver disconnect scenarios), and for scatterlist based streaming i/o (bulk or interrupt).
USB drivers need to provide buffers that can be used for DMA, although they don't necessarily need to provide the DMA mapping themselves. There are APIs to use used when allocating DMA buffers, which can prevent use of bounce buffers on some systems. In some cases, drivers may be able to rely on 64bit DMA to eliminate another kind of bounce buffer.
usb_init_urb — initializes a urb so that it can be used by a USB driver
void usb_init_urb ( | urb); |
struct urb * | urb; |
Initializes a urb so that the USB subsystem can use it properly.
If a urb is created with a call to usb_alloc_urb it is not
necessary to call this function. Only use this if you allocate the
space for a struct urb on your own. If you call this function, be
careful when freeing the memory for your urb that it is no longer in
use by the USB core.
Only use this function if you _really_ understand what you are doing.
usb_alloc_urb — creates a new urb for a USB driver to use
struct urb * usb_alloc_urb ( | iso_packets, | |
mem_flags); |
int | iso_packets; |
gfp_t | mem_flags; |
iso_packetsnumber of iso packets for this urb
mem_flags
the type of memory to allocate, see kmalloc for a list of
valid options for this.
Creates an urb for the USB driver to use, initializes a few internal structures, incrementes the usage counter, and returns a pointer to it.
If no memory is available, NULL is returned.
If the driver want to use this urb for interrupt, control, or bulk endpoints, pass '0' as the number of iso packets.
The driver must call usb_free_urb when it is finished with the urb.
usb_free_urb — frees the memory used by a urb when all users of it are finished
void usb_free_urb ( | urb); |
struct urb * | urb; |
usb_get_urb — increments the reference count of the urb
struct urb * usb_get_urb ( | urb); |
struct urb * | urb; |
usb_anchor_urb — anchors an URB while it is processed
void usb_anchor_urb ( | urb, | |
anchor); |
struct urb * | urb; |
struct usb_anchor * | anchor; |
usb_submit_urb — issue an asynchronous transfer request for an endpoint
int usb_submit_urb ( | urb, | |
mem_flags); |
struct urb * | urb; |
gfp_t | mem_flags; |
urbpointer to the urb describing the request
mem_flags
the type of memory to allocate, see kmalloc for a list
of valid options for this.
This submits a transfer request, and transfers control of the URB describing that request to the USB subsystem. Request completion will be indicated later, asynchronously, by calling the completion handler. The three types of completion are success, error, and unlink (a software-induced fault, also called “request cancellation”).
URBs may be submitted in interrupt context.
The caller must have correctly initialized the URB before submitting
it. Functions such as usb_fill_bulk_urb and usb_fill_control_urb are
available to ensure that most fields are correctly initialized, for
the particular kind of transfer, although they will not initialize
any transfer flags.
Successful submissions return 0; otherwise this routine returns a
negative error number. If the submission is successful, the complete
callback from the URB will be called exactly once, when the USB core and
Host Controller Driver (HCD) are finished with the URB. When the completion
function is called, control of the URB is returned to the device
driver which issued the request. The completion handler may then
immediately free or reuse that URB.
With few exceptions, USB device drivers should never access URB fields
provided by usbcore or the HCD until its complete is called.
The exceptions relate to periodic transfer scheduling. For both
interrupt and isochronous urbs, as part of successful URB submission
urb->interval is modified to reflect the actual transfer period used
(normally some power of two units). And for isochronous urbs,
urb->start_frame is modified to reflect when the URB's transfers were
scheduled to start. Not all isochronous transfer scheduling policies
will work, but most host controller drivers should easily handle ISO
queues going from now until 10-200 msec into the future.
For control endpoints, the synchronous usb_control_msg call is
often used (in non-interrupt context) instead of this call.
That is often used through convenience wrappers, for the requests
that are standardized in the USB 2.0 specification. For bulk
endpoints, a synchronous usb_bulk_msg call is available.
URBs may be submitted to endpoints before previous ones complete, to minimize the impact of interrupt latencies and system overhead on data throughput. With that queuing policy, an endpoint's queue would never be empty. This is required for continuous isochronous data streams, and may also be required for some kinds of interrupt transfers. Such queuing also maximizes bandwidth utilization by letting USB controllers start work on later requests before driver software has finished the completion processing for earlier (successful) requests.
As of Linux 2.6, all USB endpoint transfer queues support depths greater than one. This was previously a HCD-specific behavior, except for ISO transfers. Non-isochronous endpoint queues are inactive during cleanup after faults (transfer errors or cancellation).
Periodic transfers (interrupt or isochronous) are performed repeatedly, using the interval specified in the urb. Submitting the first urb to the endpoint reserves the bandwidth necessary to make those transfers. If the USB subsystem can't allocate sufficient bandwidth to perform the periodic request, submitting such a periodic request should fail.
For devices under xHCI, the bandwidth is reserved at configuration time, or when the alt setting is selected. If there is not enough bus bandwidth, the configuration/alt setting request will fail. Therefore, submissions to periodic endpoints on devices under xHCI should never fail due to bandwidth constraints.
Device drivers must explicitly request that repetition, by ensuring that some URB is always on the endpoint's queue (except possibly for short periods during completion callacks). When there is no longer an urb queued, the endpoint's bandwidth reservation is canceled. This means drivers can use their completion handlers to ensure they keep bandwidth they need, by reinitializing and resubmitting the just-completed urb until the driver longer needs that periodic bandwidth.
The general rules for how to decide which mem_flags to use are the same as for kmalloc. There are four different possible values; GFP_KERNEL, GFP_NOFS, GFP_NOIO and GFP_ATOMIC.
GFP_NOFS is not ever used, as it has not been implemented yet.
GFP_ATOMIC is used when (a) you are inside a completion handler, an interrupt, bottom half, tasklet or timer, or (b) you are holding a spinlock or rwlock (does not apply to semaphores), or (c) current->state != TASK_RUNNING, this is the case only after you've changed it.
GFP_NOIO is used in the block io path and error handling of storage devices.
All other situations use GFP_KERNEL.
Some more specific rules for mem_flags can be inferred, such as
(1) start_xmit, timeout, and receive methods of network drivers must
use GFP_ATOMIC (they are called with a spinlock held);
(2) queuecommand methods of scsi drivers must use GFP_ATOMIC (also
called with a spinlock held);
(3) If you use a kernel thread with a network driver you must use
GFP_NOIO, unless (b) or (c) apply;
(4) after you have done a down you can use GFP_KERNEL, unless (b) or (c)
apply or your are in a storage driver's block io path;
(5) USB probe and disconnect can use GFP_KERNEL unless (b) or (c) apply; and
(6) changing firmware on a running storage or net device uses
GFP_NOIO, unless b) or c) apply
usb_unlink_urb — abort/cancel a transfer request for an endpoint
int usb_unlink_urb ( | urb); |
struct urb * | urb; |
This routine cancels an in-progress request. URBs complete only once
per submission, and may be canceled only once per submission.
Successful cancellation means termination of urb will be expedited
and the completion handler will be called with a status code
indicating that the request has been canceled (rather than any other
code).
Drivers should not call this routine or related routines, such as
usb_kill_urb or usb_unlink_anchored_urbs, after their disconnect
method has returned. The disconnect function should synchronize with
a driver's I/O routines to insure that all URB-related activity has
completed before it returns.
This request is always asynchronous. Success is indicated by
returning -EINPROGRESS, at which time the URB will probably not yet
have been given back to the device driver. When it is eventually
called, the completion function will see urb->status == -ECONNRESET.
Failure is indicated by usb_unlink_urb returning any other value.
Unlinking will fail when urb is not currently “linked” (i.e., it was
never submitted, or it was unlinked before, or the hardware is already
finished with it), even if the completion handler has not yet run.
[The behaviors and guarantees described below do not apply to virtual root hubs but only to endpoint queues for physical USB devices.]
Host Controller Drivers (HCDs) place all the URBs for a particular endpoint in a queue. Normally the queue advances as the controller hardware processes each request. But when an URB terminates with an error its queue generally stops (see below), at least until that URB's completion routine returns. It is guaranteed that a stopped queue will not restart until all its unlinked URBs have been fully retired, with their completion routines run, even if that's not until some time after the original completion handler returns. The same behavior and guarantee apply when an URB terminates because it was unlinked.
Bulk and interrupt endpoint queues are guaranteed to stop whenever an URB terminates with any sort of error, including -ECONNRESET, -ENOENT, and -EREMOTEIO. Control endpoint queues behave the same way except that they are not guaranteed to stop for -EREMOTEIO errors. Queues for isochronous endpoints are treated differently, because they must advance at fixed rates. Such queues do not stop when an URB encounters an error or is unlinked. An unlinked isochronous URB may leave a gap in the stream of packets; it is undefined whether such gaps can be filled in.
Note that early termination of an URB because a short packet was received will generate a -EREMOTEIO error if and only if the URB_SHORT_NOT_OK flag is set. By setting this flag, USB device drivers can build deep queues for large or complex bulk transfers and clean them up reliably after any sort of aborted transfer by unlinking all pending URBs at the first fault.
When a control URB terminates with an error other than -EREMOTEIO, it is quite likely that the status stage of the transfer will not take place.
usb_kill_urb — cancel a transfer request and wait for it to finish
void usb_kill_urb ( | urb); |
struct urb * | urb; |
This routine cancels an in-progress request. It is guaranteed that
upon return all completion handlers will have finished and the URB
will be totally idle and available for reuse. These features make
this an ideal way to stop I/O in a disconnect callback or close
function. If the request has not already finished or been unlinked
the completion handler will see urb->status == -ENOENT.
While the routine is running, attempts to resubmit the URB will fail with error -EPERM. Thus even if the URB's completion handler always tries to resubmit, it will not succeed and the URB will become idle.
This routine may not be used in an interrupt context (such as a bottom
half or a completion handler), or when holding a spinlock, or in other
situations where the caller can't schedule.
This routine should not be called by a driver after its disconnect method has returned.
usb_poison_urb — reliably kill a transfer and prevent further use of an URB
void usb_poison_urb ( | urb); |
struct urb * | urb; |
This routine cancels an in-progress request. It is guaranteed that
upon return all completion handlers will have finished and the URB
will be totally idle and cannot be reused. These features make
this an ideal way to stop I/O in a disconnect callback.
If the request has not already finished or been unlinked
the completion handler will see urb->status == -ENOENT.
After and while the routine runs, attempts to resubmit the URB will fail with error -EPERM. Thus even if the URB's completion handler always tries to resubmit, it will not succeed and the URB will become idle.
This routine may not be used in an interrupt context (such as a bottom
half or a completion handler), or when holding a spinlock, or in other
situations where the caller can't schedule.
This routine should not be called by a driver after its disconnect method has returned.
usb_kill_anchored_urbs — cancel transfer requests en masse
void usb_kill_anchored_urbs ( | anchor); |
struct usb_anchor * | anchor; |
usb_poison_anchored_urbs — cease all traffic from an anchor
void usb_poison_anchored_urbs ( | anchor); |
struct usb_anchor * | anchor; |
usb_unpoison_anchored_urbs — let an anchor be used successfully again
void usb_unpoison_anchored_urbs ( | anchor); |
struct usb_anchor * | anchor; |
usb_unlink_anchored_urbs — asynchronously cancel transfer requests en masse
void usb_unlink_anchored_urbs ( | anchor); |
struct usb_anchor * | anchor; |
usb_wait_anchor_empty_timeout — wait for an anchor to be unused
int usb_wait_anchor_empty_timeout ( | anchor, | |
timeout); |
struct usb_anchor * | anchor; |
unsigned int | timeout; |
usb_get_from_anchor — get an anchor's oldest urb
struct urb * usb_get_from_anchor ( | anchor); |
struct usb_anchor * | anchor; |
usb_scuttle_anchored_urbs — unanchor all an anchor's urbs
void usb_scuttle_anchored_urbs ( | anchor); |
struct usb_anchor * | anchor; |
usb_anchor_empty — is an anchor empty
int usb_anchor_empty ( | anchor); |
struct usb_anchor * | anchor; |
usb_control_msg — Builds a control urb, sends it off and waits for completion
int usb_control_msg ( | dev, | |
| pipe, | ||
| request, | ||
| requesttype, | ||
| value, | ||
| index, | ||
| data, | ||
| size, | ||
timeout); |
struct usb_device * | dev; |
unsigned int | pipe; |
__u8 | request; |
__u8 | requesttype; |
__u16 | value; |
__u16 | index; |
void * | data; |
__u16 | size; |
int | timeout; |
devpointer to the usb device to send the message to
pipeendpoint “pipe” to send the message to
requestUSB message request value
requesttypeUSB message request type value
valueUSB message value
indexUSB message index value
datapointer to the data to send
sizelength in bytes of the data to send
timeouttime in msecs to wait for the message to complete before timing out (if 0 the wait is forever)
This function sends a simple control message to a specified endpoint and waits for the message to complete, or timeout.
If successful, it returns the number of bytes transferred, otherwise a negative error number.
Don't use this function from within an interrupt context, like a bottom half
handler. If you need an asynchronous message, or need to send a message
from within interrupt context, use usb_submit_urb.
If a thread in your driver uses this call, make sure your disconnect
method can wait for it to complete. Since you don't have a handle on the
URB used, you can't cancel the request.
usb_interrupt_msg — Builds an interrupt urb, sends it off and waits for completion
int usb_interrupt_msg ( | usb_dev, | |
| pipe, | ||
| data, | ||
| len, | ||
| actual_length, | ||
timeout); |
struct usb_device * | usb_dev; |
unsigned int | pipe; |
void * | data; |
int | len; |
int * | actual_length; |
int | timeout; |
usb_devpointer to the usb device to send the message to
pipeendpoint “pipe” to send the message to
datapointer to the data to send
lenlength in bytes of the data to send
actual_lengthpointer to a location to put the actual length transferred in bytes
timeouttime in msecs to wait for the message to complete before timing out (if 0 the wait is forever)
This function sends a simple interrupt message to a specified endpoint and waits for the message to complete, or timeout.
If successful, it returns 0, otherwise a negative error number. The number of actual bytes transferred will be stored in the actual_length paramater.
Don't use this function from within an interrupt context, like a bottom half
handler. If you need an asynchronous message, or need to send a message
from within interrupt context, use usb_submit_urb If a thread in your
driver uses this call, make sure your disconnect method can wait for it to
complete. Since you don't have a handle on the URB used, you can't cancel
the request.
usb_bulk_msg — Builds a bulk urb, sends it off and waits for completion
int usb_bulk_msg ( | usb_dev, | |
| pipe, | ||
| data, | ||
| len, | ||
| actual_length, | ||
timeout); |
struct usb_device * | usb_dev; |
unsigned int | pipe; |
void * | data; |
int | len; |
int * | actual_length; |
int | timeout; |
usb_devpointer to the usb device to send the message to
pipeendpoint “pipe” to send the message to
datapointer to the data to send
lenlength in bytes of the data to send
actual_lengthpointer to a location to put the actual length transferred in bytes
timeouttime in msecs to wait for the message to complete before timing out (if 0 the wait is forever)
This function sends a simple bulk message to a specified endpoint and waits for the message to complete, or timeout.
If successful, it returns 0, otherwise a negative error number. The number of actual bytes transferred will be stored in the actual_length paramater.
Don't use this function from within an interrupt context, like a bottom half
handler. If you need an asynchronous message, or need to send a message
from within interrupt context, use usb_submit_urb If a thread in your
driver uses this call, make sure your disconnect method can wait for it to
complete. Since you don't have a handle on the URB used, you can't cancel
the request.
Because there is no usb_interrupt_msg and no USBDEVFS_INTERRUPT ioctl,
users are forced to abuse this routine by using it to submit URBs for
interrupt endpoints. We will take the liberty of creating an interrupt URB
(with the default interval) if the target is an interrupt endpoint.
usb_sg_init — initializes scatterlist-based bulk/interrupt I/O request
int usb_sg_init ( | io, | |
| dev, | ||
| pipe, | ||
| period, | ||
| sg, | ||
| nents, | ||
| length, | ||
mem_flags); |
struct usb_sg_request * | io; |
struct usb_device * | dev; |
unsigned | pipe; |
unsigned | period; |
struct scatterlist * | sg; |
int | nents; |
size_t | length; |
gfp_t | mem_flags; |
io
request block being initialized. until usb_sg_wait returns,
treat this as a pointer to an opaque block of memory,
devthe usb device that will send or receive the data
pipeendpoint “pipe” used to transfer the data
periodpolling rate for interrupt endpoints, in frames or (for high speed endpoints) microframes; ignored for bulk
sgscatterlist entries
nentshow many entries in the scatterlist
lengthhow many bytes to send from the scatterlist, or zero to send every byte identified in the list.
mem_flagsSLAB_* flags affecting memory allocations in this call
Returns zero for success, else a negative errno value. This initializes a scatter/gather request, allocating resources such as I/O mappings and urb memory (except maybe memory used by USB controller drivers).
The request must be issued using usb_sg_wait, which waits for the I/O to
complete (or to be canceled) and then cleans up all resources allocated by
usb_sg_init.
The request may be canceled with usb_sg_cancel, either before or after
usb_sg_wait is called.
usb_sg_wait — synchronously execute scatter/gather request
void usb_sg_wait ( | io); |
struct usb_sg_request * | io; |
io
request block handle, as initialized with usb_sg_init.
some fields become accessible when this call returns.
This function blocks until the specified I/O operation completes. It leverages the grouping of the related I/O requests to get good transfer rates, by queueing the requests. At higher speeds, such queuing can significantly improve USB throughput.
There are three kinds of completion for this function.
(1) success, where io->status is zero. The number of io->bytes
transferred is as requested.
(2) error, where io->status is a negative errno value. The number
of io->bytes transferred before the error is usually less
than requested, and can be nonzero.
(3) cancellation, a type of error with status -ECONNRESET that
is initiated by usb_sg_cancel.
When this function returns, all memory allocated through usb_sg_init or
this call will have been freed. The request block parameter may still be
passed to usb_sg_cancel, or it may be freed. It could also be
reinitialized and then reused.
Bulk transfers are valid for full or high speed endpoints. The best full speed data rate is 19 packets of 64 bytes each per frame, or 1216 bytes per millisecond. The best high speed data rate is 13 packets of 512 bytes each per microframe, or 52 KBytes per millisecond.
The reason to use interrupt transfers through this API would most likely be to reserve high speed bandwidth, where up to 24 KBytes per millisecond could be transferred. That capability is less useful for low or full speed interrupt endpoints, which allow at most one packet per millisecond, of at most 8 or 64 bytes (respectively).
It is not necessary to call this function to reserve bandwidth for devices under an xHCI host controller, as the bandwidth is reserved when the configuration or interface alt setting is selected.
usb_sg_cancel —
stop scatter/gather i/o issued by usb_sg_wait
void usb_sg_cancel ( | io); |
struct usb_sg_request * | io; |
usb_get_descriptor — issues a generic GET_DESCRIPTOR request
int usb_get_descriptor ( | dev, | |
| type, | ||
| index, | ||
| buf, | ||
size); |
struct usb_device * | dev; |
unsigned char | type; |
unsigned char | index; |
void * | buf; |
int | size; |
devthe device whose descriptor is being retrieved
typethe descriptor type (USB_DT_*)
indexthe number of the descriptor
bufwhere to put the descriptor
sizehow big is “buf”?
Gets a USB descriptor. Convenience functions exist to simplify
getting some types of descriptors. Use
usb_get_string or usb_string for USB_DT_STRING.
Device (USB_DT_DEVICE) and configuration descriptors (USB_DT_CONFIG)
are part of the device structure.
In addition to a number of USB-standard descriptors, some
devices also use class-specific or vendor-specific descriptors.
This call is synchronous, and may not be used in an interrupt context.
Returns the number of bytes received on success, or else the status code
returned by the underlying usb_control_msg call.
usb_string — returns UTF-8 version of a string descriptor
int usb_string ( | dev, | |
| index, | ||
| buf, | ||
size); |
struct usb_device * | dev; |
int | index; |
char * | buf; |
size_t | size; |
devthe device whose string descriptor is being retrieved
indexthe number of the descriptor
bufwhere to put the string
sizehow big is “buf”?
This converts the UTF-16LE encoded strings returned by devices, from
usb_get_string_descriptor, to null-terminated UTF-8 encoded ones
that are more usable in most kernel contexts. Note that this function
chooses strings in the first language supported by the device.
This call is synchronous, and may not be used in an interrupt context.
Returns length of the string (>= 0) or usb_control_msg status (< 0).
usb_get_status — issues a GET_STATUS call
int usb_get_status ( | dev, | |
| type, | ||
| target, | ||
data); |
struct usb_device * | dev; |
int | type; |
int | target; |
void * | data; |
devthe device whose status is being checked
typeUSB_RECIP_*; for device, interface, or endpoint
targetzero (for device), else interface or endpoint number
datapointer to two bytes of bitmap data
Returns device, interface, or endpoint status. Normally only of interest to see if the device is self powered, or has enabled the remote wakeup facility; or whether a bulk or interrupt endpoint is halted (“stalled”).
Bits in these status bitmaps are set using the SET_FEATURE request,
and cleared using the CLEAR_FEATURE request. The usb_clear_halt
function should be used to clear halt (“stall”) status.
This call is synchronous, and may not be used in an interrupt context.
Returns the number of bytes received on success, or else the status code
returned by the underlying usb_control_msg call.
usb_clear_halt — tells device to clear endpoint halt/stall condition
int usb_clear_halt ( | dev, | |
pipe); |
struct usb_device * | dev; |
int | pipe; |
This is used to clear halt conditions for bulk and interrupt endpoints, as reported by URB completion status. Endpoints that are halted are sometimes referred to as being “stalled”. Such endpoints are unable to transmit or receive data until the halt status is cleared. Any URBs queued for such an endpoint should normally be unlinked by the driver before clearing the halt condition, as described in sections 5.7.5 and 5.8.5 of the USB 2.0 spec.
Note that control and isochronous endpoints don't halt, although control endpoints report “protocol stall” (for unsupported requests) using the same status code used to report a true stall.
This call is synchronous, and may not be used in an interrupt context.
Returns zero on success, or else the status code returned by the
underlying usb_control_msg call.
usb_reset_endpoint — Reset an endpoint's state.
void usb_reset_endpoint ( | dev, | |
epaddr); |
struct usb_device * | dev; |
unsigned int | epaddr; |
usb_set_interface — Makes a particular alternate setting be current
int usb_set_interface ( | dev, | |
| interface, | ||
alternate); |
struct usb_device * | dev; |
int | interface; |
int | alternate; |
devthe device whose interface is being updated
interfacethe interface being updated
alternatethe setting being chosen.
This is used to enable data transfers on interfaces that may not be enabled by default. Not all devices support such configurability. Only the driver bound to an interface may change its setting.
Within any given configuration, each interface may have several alternative settings. These are often used to control levels of bandwidth consumption. For example, the default setting for a high speed interrupt endpoint may not send more than 64 bytes per microframe, while interrupt transfers of up to 3KBytes per microframe are legal. Also, isochronous endpoints may never be part of an interface's default setting. To access such bandwidth, alternate interface settings must be made current.
Note that in the Linux USB subsystem, bandwidth associated with an endpoint in a given alternate setting is not reserved until an URB is submitted that needs that bandwidth. Some other operating systems allocate bandwidth early, when a configuration is chosen.
This call is synchronous, and may not be used in an interrupt context. Also, drivers must not change altsettings while urbs are scheduled for endpoints in that interface; all such urbs must first be completed (perhaps forced by unlinking).
Returns zero on success, or else the status code returned by the
underlying usb_control_msg call.
usb_reset_configuration — lightweight device reset
int usb_reset_configuration ( | dev); |
struct usb_device * | dev; |
This issues a standard SET_CONFIGURATION request to the device using the current configuration. The effect is to reset most USB-related state in the device, including interface altsettings (reset to zero), endpoint halts (cleared), and endpoint state (only for bulk and interrupt endpoints). Other usbcore state is unchanged, including bindings of usb device drivers to interfaces.
Because this affects multiple interfaces, avoid using this with composite
(multi-interface) devices. Instead, the driver for each interface may
use usb_set_interface on the interfaces it claims. Be careful though;
some devices don't support the SET_INTERFACE request, and others won't
reset all the interface state (notably endpoint state). Resetting the whole
configuration would affect other drivers' interfaces.
The caller must own the device lock.
Returns zero on success, else a negative error code.
usb_driver_set_configuration — Provide a way for drivers to change device configurations
int usb_driver_set_configuration ( | udev, | |
config); |
struct usb_device * | udev; |
int | config; |
udevthe device whose configuration is being updated
configthe configuration being chosen.
Device interface drivers are not allowed to change device configurations. This is because changing configurations will destroy the interface the driver is bound to and create new ones; it would be like a floppy-disk driver telling the computer to replace the floppy-disk drive with a tape drive!
Still, in certain specialized circumstances the need may arise. This routine gets around the normal restrictions by using a work thread to submit the change-config request.
Returns 0 if the request was succesfully queued, error code otherwise. The caller has no way to know whether the queued request will eventually succeed.
usb_register_dev — register a USB device, and ask for a minor number
int usb_register_dev ( | intf, | |
class_driver); |
struct usb_interface * | intf; |
struct usb_class_driver * | class_driver; |
intfpointer to the usb_interface that is being registered
class_driverpointer to the usb_class_driver for this device
This should be called by all USB drivers that use the USB major number. If CONFIG_USB_DYNAMIC_MINORS is enabled, the minor number will be dynamically allocated out of the list of available ones. If it is not enabled, the minor number will be based on the next available free minor, starting at the class_driver->minor_base.
This function also creates a usb class device in the sysfs tree.
usb_deregister_dev must be called when the driver is done with
the minor numbers given out by this function.
Returns -EINVAL if something bad happens with trying to register a device, and 0 on success.
usb_deregister_dev — deregister a USB device's dynamic minor.
void usb_deregister_dev ( | intf, | |
class_driver); |
struct usb_interface * | intf; |
struct usb_class_driver * | class_driver; |
intfpointer to the usb_interface that is being deregistered
class_driverpointer to the usb_class_driver for this device
Used in conjunction with usb_register_dev. This function is called
when the USB driver is finished with the minor numbers gotten from a
call to usb_register_dev (usually when the device is disconnected
from the system.)
This function also removes the usb class device from the sysfs tree.
This should be called by all drivers that use the USB major number.
usb_driver_claim_interface — bind a driver to an interface
int usb_driver_claim_interface ( | driver, | |
| iface, | ||
priv); |
struct usb_driver * | driver; |
struct usb_interface * | iface; |
void * | priv; |
driverthe driver to be bound
ifacethe interface to which it will be bound; must be in the usb device's active configuration
privdriver data associated with that interface
This is used by usb device drivers that need to claim more than one interface on a device when probing (audio and acm are current examples). No device driver should directly modify internal usb_interface or usb_device structure members.
Few drivers should need to use this routine, since the most natural
way to bind to an interface is to return the private data from
the driver's probe method.
Callers must own the device lock, so driver probe entries don't need
extra locking, but other call contexts may need to explicitly claim that
lock.
usb_driver_release_interface — unbind a driver from an interface
void usb_driver_release_interface ( | driver, | |
iface); |
struct usb_driver * | driver; |
struct usb_interface * | iface; |
This can be used by drivers to release an interface without waiting
for their disconnect methods to be called. In typical cases this
also causes the driver disconnect method to be called.
This call is synchronous, and may not be used in an interrupt context.
Callers must own the device lock, so driver disconnect entries don't
need extra locking, but other call contexts may need to explicitly claim
that lock.
usb_match_id — find first usb_device_id matching device or interface
const struct usb_device_id * usb_match_id ( | interface, | |
id); |
struct usb_interface * | interface; |
const struct usb_device_id * | id; |
interfacethe interface of interest
idarray of usb_device_id structures, terminated by zero entry
usb_match_id searches an array of usb_device_id's and returns the first one matching the device or interface, or null. This is used when binding (or rebinding) a driver to an interface. Most USB device drivers will use this indirectly, through the usb core, but some layered driver frameworks use it directly. These device tables are exported with MODULE_DEVICE_TABLE, through modutils, to support the driver loading functionality of USB hotplugging.
The “match_flags” element in a usb_device_id controls which members are used. If the corresponding bit is set, the value in the device_id must match its corresponding member in the device or interface descriptor, or else the device_id does not match.
“driver_info” is normally used only by device drivers,
but you can create a wildcard “matches anything” usb_device_id
as a driver's “modules.usbmap” entry if you provide an id with
only a nonzero “driver_info” field. If you do this, the USB device
driver's probe routine should use additional intelligence to
decide whether to bind to the specified interface.
The match algorithm is very simple, so that intelligence in driver selection must come from smart driver id records. Unless you have good reasons to use another selection policy, provide match elements only in related groups, and order match specifiers from specific to general. Use the macros provided for that purpose if you can.
The most specific match specifiers use device descriptor data. These are commonly used with product-specific matches; the USB_DEVICE macro lets you provide vendor and product IDs, and you can also match against ranges of product revisions. These are widely used for devices with application or vendor specific bDeviceClass values.
Matches based on device class/subclass/protocol specifications are slightly more general; use the USB_DEVICE_INFO macro, or its siblings. These are used with single-function devices where bDeviceClass doesn't specify that each interface has its own class.
Matches based on interface class/subclass/protocol are the most general; they let drivers bind to any interface on a multiple-function device. Use the USB_INTERFACE_INFO macro, or its siblings, to match class-per-interface style devices (as recorded in bInterfaceClass).
Note that an entry created by USB_INTERFACE_INFO won't match any interface if the device class is set to Vendor-Specific. This is deliberate; according to the USB spec the meanings of the interface class/subclass/protocol for these devices are also vendor-specific, and hence matching against a standard product class wouldn't work anyway. If you really want to use an interface-based match for such a device, create a match record that also specifies the vendor ID. (Unforunately there isn't a standard macro for creating records like this.)
Within those groups, remember that not all combinations are meaningful. For example, don't give a product version range without vendor and product IDs; or specify a protocol without its associated class and subclass.
usb_register_device_driver — register a USB device (not interface) driver
int usb_register_device_driver ( | new_udriver, | |
owner); |
struct usb_device_driver * | new_udriver; |
struct module * | owner; |
usb_deregister_device_driver — unregister a USB device (not interface) driver
void usb_deregister_device_driver ( | udriver); |
struct usb_device_driver * | udriver; |
usb_register_driver — register a USB interface driver
int usb_register_driver ( | new_driver, | |
| owner, | ||
mod_name); |
struct usb_driver * | new_driver; |
struct module * | owner; |
const char * | mod_name; |
new_driverUSB operations for the interface driver
ownermodule owner of this driver.
mod_namemodule name string
usb_deregister — unregister a USB interface driver
void usb_deregister ( | driver); |
struct usb_driver * | driver; |
usb_autopm_put_interface — decrement a USB interface's PM-usage counter
void usb_autopm_put_interface ( | intf); |
struct usb_interface * | intf; |
This routine should be called by an interface driver when it is
finished using intf and wants to allow it to autosuspend. A typical
example would be a character-device driver when its device file is
closed.
The routine decrements intf's usage counter. When the counter reaches
0, a delayed autosuspend request for intf's device is queued. When
the delay expires, if intf->pm_usage_cnt is still <= 0 along with all
the other usage counters for the sibling interfaces and intf's
usb_device, the device and all its interfaces will be autosuspended.
Note that intf->pm_usage_cnt is owned by the interface driver. The
core will not change its value other than the increment and decrement
in usb_autopm_get_interface and usb_autopm_put_interface. The driver
may use this simple counter-oriented discipline or may set the value
any way it likes.
If the driver has set intf->needs_remote_wakeup then autosuspend will
take place only if the device's remote-wakeup facility is enabled.
Suspend method calls queued by this routine can arrive at any time
while intf is resumed and its usage counter is equal to 0. They are
not protected by the usb_device's lock but only by its pm_mutex.
Drivers must provide their own synchronization.
This routine can run only in process context.
usb_autopm_put_interface_async — decrement a USB interface's PM-usage counter
void usb_autopm_put_interface_async ( | intf); |
struct usb_interface * | intf; |
This routine does essentially the same thing as
usb_autopm_put_interface: it decrements intf's usage counter and
queues a delayed autosuspend request if the counter is <= 0. The
difference is that it does not acquire the device's pm_mutex;
callers must handle all synchronization issues themselves.
Typically a driver would call this routine during an URB's completion handler, if no more URBs were pending.
This routine can run in atomic context.
usb_autopm_get_interface — increment a USB interface's PM-usage counter
int usb_autopm_get_interface ( | intf); |
struct usb_interface * | intf; |
This routine should be called by an interface driver when it wants to
use intf and needs to guarantee that it is not suspended. In addition,
the routine prevents intf from being autosuspended subsequently. (Note
that this will not prevent suspend events originating in the PM core.)
This prevention will persist until usb_autopm_put_interface is called
or intf is unbound. A typical example would be a character-device
driver when its device file is opened.
The routine increments intf's usage counter. (However if the
autoresume fails then the counter is re-decremented.) So long as the
counter is greater than 0, autosuspend will not be allowed for intf
or its usb_device. When the driver is finished using intf it should
call usb_autopm_put_interface to decrement the usage counter and
queue a delayed autosuspend request (if the counter is <= 0).
Note that intf->pm_usage_cnt is owned by the interface driver. The
core will not change its value other than the increment and decrement
in usb_autopm_get_interface and usb_autopm_put_interface. The driver
may use this simple counter-oriented discipline or may set the value
any way it likes.
Resume method calls generated by this routine can arrive at any time
while intf is suspended. They are not protected by the usb_device's
lock but only by its pm_mutex. Drivers must provide their own
synchronization.
This routine can run only in process context.
usb_autopm_get_interface_async — increment a USB interface's PM-usage counter
int usb_autopm_get_interface_async ( | intf); |
struct usb_interface * | intf; |
This routine does much the same thing as
usb_autopm_get_interface: it increments intf's usage counter and
queues an autoresume request if the result is > 0. The differences
are that it does not acquire the device's pm_mutex (callers must
handle all synchronization issues themselves), and it does not
autoresume the device directly (it only queues a request). After a
successful call, the device will generally not yet be resumed.
This routine can run in atomic context.
usb_autopm_set_interface — set a USB interface's autosuspend state
int usb_autopm_set_interface ( | intf); |
struct usb_interface * | intf; |
This routine sets the autosuspend state of intf's device according
to intf's usage counter, which the caller must have set previously.
If the counter is <= 0, the device is autosuspended (if it isn't
already suspended and if nothing else prevents the autosuspend). If
the counter is > 0, the device is autoresumed (if it isn't already
awake).
usb_ifnum_to_if — get the interface object with a given interface number
struct usb_interface * usb_ifnum_to_if ( | dev, | |
ifnum); |
const struct usb_device * | dev; |
unsigned | ifnum; |
This walks the device descriptor for the currently active configuration and returns a pointer to the interface with that particular interface number, or null.
Note that configuration descriptors are not required to assign interface numbers sequentially, so that it would be incorrect to assume that the first interface in that descriptor corresponds to interface zero. This routine helps device drivers avoid such mistakes. However, you should make sure that you do the right thing with any alternate settings available for this interfaces.
Don't call this function unless you are bound to one of the interfaces on this device or you have locked the device!
usb_altnum_to_altsetting — get the altsetting structure with a given alternate setting number.
struct usb_host_interface * usb_altnum_to_altsetting ( | intf, | |
altnum); |
const struct usb_interface * | intf; |
unsigned int | altnum; |
intfthe interface containing the altsetting in question
altnumthe desired alternate setting number
This searches the altsetting array of the specified interface for an entry with the correct bAlternateSetting value and returns a pointer to that entry, or null.
Note that altsettings need not be stored sequentially by number, so it would be incorrect to assume that the first altsetting entry in the array corresponds to altsetting zero. This routine helps device drivers avoid such mistakes.
Don't call this function unless you are bound to the intf interface or you have locked the device!
usb_find_interface — find usb_interface pointer for driver and device
struct usb_interface * usb_find_interface ( | drv, | |
minor); |
struct usb_driver * | drv; |
int | minor; |
usb_get_dev — increments the reference count of the usb device structure
struct usb_device * usb_get_dev ( | dev); |
struct usb_device * | dev; |
Each live reference to a device should be refcounted.
Drivers for USB interfaces should normally record such references in
their probe methods, when they bind to an interface, and release
them by calling usb_put_dev, in their disconnect methods.
A pointer to the device with the incremented reference counter is returned.
usb_put_dev — release a use of the usb device structure
void usb_put_dev ( | dev); |
struct usb_device * | dev; |
usb_get_intf — increments the reference count of the usb interface structure
struct usb_interface * usb_get_intf ( | intf); |
struct usb_interface * | intf; |
Each live reference to a interface must be refcounted.
Drivers for USB interfaces should normally record such references in
their probe methods, when they bind to an interface, and release
them by calling usb_put_intf, in their disconnect methods.
A pointer to the interface with the incremented reference counter is returned.
usb_put_intf — release a use of the usb interface structure
void usb_put_intf ( | intf); |
struct usb_interface * | intf; |
usb_lock_device_for_reset — cautiously acquire the lock for a usb device structure
int usb_lock_device_for_reset ( | udev, | |
iface); |
struct usb_device * | udev; |
const struct usb_interface * | iface; |
udevdevice that's being locked
ifaceinterface bound to the driver making the request (optional)
Attempts to acquire the device lock, but fails if the device is
NOTATTACHED or SUSPENDED, or if iface is specified and the interface
is neither BINDING nor BOUND. Rather than sleeping to wait for the
lock, the routine polls repeatedly. This is to prevent deadlock with
disconnect; in some drivers (such as usb-storage) the disconnect
or suspend method will block waiting for a device reset to complete.
Returns a negative error code for failure, otherwise 0.
usb_get_current_frame_number — return current bus frame number
int usb_get_current_frame_number ( | dev); |
struct usb_device * | dev; |
Returns the current frame number for the USB host controller used with the given USB device. This can be used when scheduling isochronous requests.
Note that different kinds of host controller have different “scheduling horizons”. While one type might support scheduling only 32 frames into the future, others could support scheduling up to 1024 frames into the future.
usb_buffer_alloc — allocate dma-consistent buffer for URB_NO_xxx_DMA_MAP
void * usb_buffer_alloc ( | dev, | |
| size, | ||
| mem_flags, | ||
dma); |
struct usb_device * | dev; |
size_t | size; |
gfp_t | mem_flags; |
dma_addr_t * | dma; |
devdevice the buffer will be used with
sizerequested buffer size
mem_flagsaffect whether allocation may block
dmaused to return DMA address of buffer
Return value is either null (indicating no buffer could be allocated), or the cpu-space pointer to a buffer that may be used to perform DMA to the specified device. Such cpu-space buffers are returned along with the DMA address (through the pointer provided).
These buffers are used with URB_NO_xxx_DMA_MAP set in urb->transfer_flags to avoid behaviors like using “DMA bounce buffers”, or thrashing IOMMU hardware during URB completion/resubmit. The implementation varies between platforms, depending on details of how DMA will work to this device. Using these buffers also eliminates cacheline sharing problems on architectures where CPU caches are not DMA-coherent. On systems without bus-snooping caches, these buffers are uncached.
When the buffer is no longer used, free it with usb_buffer_free.
usb_buffer_free —
free memory allocated with usb_buffer_alloc
void usb_buffer_free ( | dev, | |
| size, | ||
| addr, | ||
dma); |
struct usb_device * | dev; |
size_t | size; |
void * | addr; |
dma_addr_t | dma; |
usb_buffer_map — create DMA mapping(s) for an urb
struct urb * usb_buffer_map ( | urb); |
struct urb * | urb; |
Return value is either null (indicating no buffer could be mapped), or the parameter. URB_NO_TRANSFER_DMA_MAP and URB_NO_SETUP_DMA_MAP are added to urb->transfer_flags if the operation succeeds. If the device is connected to this system through a non-DMA controller, this operation always succeeds.
This call would normally be used for an urb which is reused, perhaps
as the target of a large periodic transfer, with usb_buffer_dmasync
calls to synchronize memory and dma state.
Reverse the effect of this call with usb_buffer_unmap.
usb_buffer_dmasync — synchronize DMA and CPU view of buffer(s)
void usb_buffer_dmasync ( | urb); |
struct urb * | urb; |
usb_buffer_unmap — free DMA mapping(s) for an urb
void usb_buffer_unmap ( | urb); |
struct urb * | urb; |
usb_buffer_map_sg — create scatterlist DMA mapping(s) for an endpoint
int usb_buffer_map_sg ( | dev, | |
| is_in, | ||
| sg, | ||
nents); |
const struct usb_device * | dev; |
int | is_in; |
struct scatterlist * | sg; |
int | nents; |
devdevice to which the scatterlist will be mapped
is_inmapping transfer direction
sgthe scatterlist to map
nentsthe number of entries in the scatterlist
Return value is either < 0 (indicating no buffers could be mapped), or the number of DMA mapping array entries in the scatterlist.
The caller is responsible for placing the resulting DMA addresses from the scatterlist into URB transfer buffer pointers, and for setting the URB_NO_TRANSFER_DMA_MAP transfer flag in each of those URBs.
Top I/O rates come from queuing URBs, instead of waiting for each one to complete before starting the next I/O. This is particularly easy to do with scatterlists. Just allocate and submit one URB for each DMA mapping entry returned, stopping on the first error or when all succeed. Better yet, use the usb_sg_*() calls, which do that (and more) for you.
This call would normally be used when translating scatterlist requests,
rather than usb_buffer_map, since on some hardware (with IOMMUs) it
may be able to coalesce mappings for improved I/O efficiency.
Reverse the effect of this call with usb_buffer_unmap_sg.
usb_buffer_dmasync_sg — synchronize DMA and CPU view of scatterlist buffer(s)
void usb_buffer_dmasync_sg ( | dev, | |
| is_in, | ||
| sg, | ||
n_hw_ents); |
const struct usb_device * | dev; |
int | is_in; |
struct scatterlist * | sg; |
int | n_hw_ents; |
usb_buffer_unmap_sg — free DMA mapping(s) for a scatterlist
void usb_buffer_unmap_sg ( | dev, | |
| is_in, | ||
| sg, | ||
n_hw_ents); |
const struct usb_device * | dev; |
int | is_in; |
struct scatterlist * | sg; |
int | n_hw_ents; |
usb_hub_clear_tt_buffer — clear control/bulk TT state in high speed hub
int usb_hub_clear_tt_buffer ( | urb); |
struct urb * | urb; |
High speed HCDs use this to tell the hub driver that some split control or bulk transaction failed in a way that requires clearing internal state of a transaction translator. This is normally detected (and reported) from interrupt context.
It may not be possible for that hub to handle additional full (or low) speed transactions until that state is fully cleared out.
usb_set_device_state — change a device's current state (usbcore, hcds)
void usb_set_device_state ( | udev, | |
new_state); |
struct usb_device * | udev; |
enum usb_device_state | new_state; |
udevpointer to device whose state should be changed
new_statenew state value to be stored
udev->state is _not_ fully protected by the device lock. Although most transitions are made only while holding the lock, the state can can change to USB_STATE_NOTATTACHED at almost any time. This is so that devices can be marked as disconnected as soon as possible, without having to wait for any semaphores to be released. As a result, all changes to any device's state must be protected by the device_state_lock spinlock.
Once a device has been added to the device tree, all changes to its state should be made using this routine. The state should _not_ be set directly.
If udev->state is already USB_STATE_NOTATTACHED then no change is made. Otherwise udev->state is set to new_state, and if new_state is USB_STATE_NOTATTACHED then all of udev's descendants' states are also set to USB_STATE_NOTATTACHED.
usb_root_hub_lost_power — called by HCD if the root hub lost Vbus power
void usb_root_hub_lost_power ( | rhdev); |
struct usb_device * | rhdev; |
The USB host controller driver calls this function when its root hub
is resumed and Vbus power has been interrupted or the controller
has been reset. The routine marks rhdev as having lost power.
When the hub driver is resumed it will take notice and carry out
power-session recovery for all the “USB-PERSIST”-enabled child devices;
the others will be disconnected.
usb_reset_device — warn interface drivers and perform a USB port reset
int usb_reset_device ( | udev); |
struct usb_device * | udev; |
Warns all drivers bound to registered interfaces (using their pre_reset method), performs the port reset, and then lets the drivers know that the reset is over (using their post_reset method).
Return value is the same as for usb_reset_and_verify_device.
The caller must own the device lock. For example, it's safe to use
this from a driver probe routine after downloading new firmware.
For calls that might not occur during probe, drivers should lock
the device using usb_lock_device_for_reset.
If an interface is currently being probed or disconnected, we assume its driver knows how to handle resets. For all other interfaces, if the driver doesn't have pre_reset and post_reset methods then we attempt to unbind it and rebind afterward.
usb_queue_reset_device — Reset a USB device from an atomic context
void usb_queue_reset_device ( | iface); |
struct usb_interface * | iface; |
This function can be used to reset a USB device from an atomic
context, where usb_reset_device won't work (as it blocks).
Doing a reset via this method is functionally equivalent to calling
usb_reset_device, except for the fact that it is delayed to a
workqueue. This means that any drivers bound to other interfaces
might be unbound, as well as users from usbfs in user space.
- Scheduling two resets at the same time from two different drivers
attached to two different interfaces of the same device is
possible; depending on how the driver attached to each interface
handles ->pre_reset, the second reset might happen or not.
- If a driver is unbound and it had a pending reset, the reset will be cancelled.
- This function can be called during .probe or .disconnect
times. On return from .disconnect, any pending resets will be
cancelled.
There is no no need to lock/unlock the reset_ws as schedule_work
does its own.
We don't do any reference count tracking because it is not needed. The lifecycle of the work_struct is tied to the usb_interface. Before destroying the interface we cancel the work_struct, so the fact that work_struct is queued and or running means the interface (and thus, the device) exist and are referenced.
Table of Contents
These APIs are only for use by host controller drivers, most of which implement standard register interfaces such as EHCI, OHCI, or UHCI. UHCI was one of the first interfaces, designed by Intel and also used by VIA; it doesn't do much in hardware. OHCI was designed later, to have the hardware do more work (bigger transfers, tracking protocol state, and so on). EHCI was designed with USB 2.0; its design has features that resemble OHCI (hardware does much more work) as well as UHCI (some parts of ISO support, TD list processing).
There are host controllers other than the "big three", although most PCI based controllers (and a few non-PCI based ones) use one of those interfaces. Not all host controllers use DMA; some use PIO, and there is also a simulator.
The same basic APIs are available to drivers for all those controllers. For historical reasons they are in two layers: struct usb_bus is a rather thin layer that became available in the 2.2 kernels, while struct usb_hcd is a more featureful layer (available in later 2.4 kernels and in 2.5) that lets HCDs share common code, to shrink driver size and significantly reduce hcd-specific behaviors.
usb_calc_bus_time — approximate periodic transaction time in nanoseconds
long usb_calc_bus_time ( | speed, | |
| is_input, | ||
| isoc, | ||
bytecount); |
int | speed; |
int | is_input; |
int | isoc; |
int | bytecount; |
usb_hcd_link_urb_to_ep — add an URB to its endpoint queue
int usb_hcd_link_urb_to_ep ( | hcd, | |
urb); |
struct usb_hcd * | hcd; |
struct urb * | urb; |
Host controller drivers should call this routine in their enqueue
method. The HCD's private spinlock must be held and interrupts must
be disabled. The actions carried out here are required for URB
submission, as well as for endpoint shutdown and for usb_kill_urb.
Returns 0 for no error, otherwise a negative error code (in which case
the enqueue method must fail). If no error occurs but enqueue fails
anyway, it must call usb_hcd_unlink_urb_from_ep before releasing
the private spinlock and returning.
usb_hcd_check_unlink_urb — check whether an URB may be unlinked
int usb_hcd_check_unlink_urb ( | hcd, | |
| urb, | ||
status); |
struct usb_hcd * | hcd; |
struct urb * | urb; |
int | status; |
hcd
host controller to which urb was submitted
urbURB being checked for unlinkability
status
error code to store in urb if the unlink succeeds
Host controller drivers should call this routine in their dequeue
method. The HCD's private spinlock must be held and interrupts must
be disabled. The actions carried out here are required for making
sure than an unlink is valid.
Returns 0 for no error, otherwise a negative error code (in which case
the dequeue method must fail). The possible error codes are:
-EIDRM: urb was not submitted or has already completed.
The completion function may not have been called yet.
-EBUSY: urb has already been unlinked.
usb_hcd_unlink_urb_from_ep — remove an URB from its endpoint queue
void usb_hcd_unlink_urb_from_ep ( | hcd, | |
urb); |
struct usb_hcd * | hcd; |
struct urb * | urb; |
usb_hcd_giveback_urb — return URB from HCD to device driver
void usb_hcd_giveback_urb ( | hcd, | |
| urb, | ||
status); |
struct usb_hcd * | hcd; |
struct urb * | urb; |
int | status; |
hcdhost controller returning the URB
urburb being returned to the USB device driver.
statuscompletion status code for the URB.
This hands the URB from HCD to its USB device driver, using its completion function. The HCD has freed all per-urb resources (and is done using urb->hcpriv). It also released all HCD locks; the device driver won't cause problems if it frees, modifies, or resubmits this URB.
If urb was unlinked, the value of status will be overridden by
urb->unlinked. Erroneous short transfers are detected in case
the HCD hasn't checked for them.
usb_hcd_resume_root_hub — called by HCD to resume its root hub
void usb_hcd_resume_root_hub ( | hcd); |
struct usb_hcd * | hcd; |
usb_bus_start_enum — start immediate enumeration (for OTG)
int usb_bus_start_enum ( | bus, | |
port_num); |
struct usb_bus * | bus; |
unsigned | port_num; |
usb_hc_died — report abnormal shutdown of a host controller (bus glue)
void usb_hc_died ( | hcd); |
struct usb_hcd * | hcd; |
usb_create_hcd — create and initialize an HCD structure
struct usb_hcd * usb_create_hcd ( | driver, | |
| dev, | ||
bus_name); |
const struct hc_driver * | driver; |
struct device * | dev; |
const char * | bus_name; |
usb_add_hcd — finish generic HCD structure initialization and register
int usb_add_hcd ( | hcd, | |
| irqnum, | ||
irqflags); |
struct usb_hcd * | hcd; |
unsigned int | irqnum; |
unsigned long | irqflags; |
usb_remove_hcd — shutdown processing for generic HCDs
void usb_remove_hcd ( | hcd); |
struct usb_hcd * | hcd; |
usb_hcd_pci_probe — initialize PCI-based HCDs
int usb_hcd_pci_probe ( | dev, | |
id); |
struct pci_dev * | dev; |
const struct pci_device_id * | id; |
usb_hcd_pci_remove — shutdown processing for PCI-based HCDs
void usb_hcd_pci_remove ( | dev); |
struct pci_dev * | dev; |
usb_hcd_pci_shutdown — shutdown host controller
void usb_hcd_pci_shutdown ( | dev); |
struct pci_dev * | dev; |
hcd_buffer_create — initialize buffer pools
int hcd_buffer_create ( | hcd); |
struct usb_hcd * | hcd; |
Call this as part of initializing a host controller that uses the dma memory allocators. It initializes some pools of dma-coherent memory that will be shared by all drivers using that controller, or returns a negative errno value on error.
Call hcd_buffer_destroy to clean up after using those pools.
Table of Contents
This chapter presents the Linux usbfs. You may prefer to avoid writing new kernel code for your USB driver; that's the problem that usbfs set out to solve. User mode device drivers are usually packaged as applications or libraries, and may use usbfs through some programming library that wraps it. Such libraries include libusb for C/C++, and jUSB for Java.
This particular documentation is incomplete, especially with respect to the asynchronous mode. As of kernel 2.5.66 the code and this (new) documentation need to be cross-reviewed.
Configure usbfs into Linux kernels by enabling the USB filesystem option (CONFIG_USB_DEVICEFS), and you get basic support for user mode USB device drivers. Until relatively recently it was often (confusingly) called usbdevfs although it wasn't solving what devfs was. Every USB device will appear in usbfs, regardless of whether or not it has a kernel driver.
Conventionally mounted at
/proc/bus/usb, usbfs
features include:
/proc/bus/usb/devices
... a text file
showing each of the USB devices on known to the kernel,
and their configuration descriptors.
You can also poll() this to learn about new devices.
/proc/bus/usb/BBB/DDD
... magic files
exposing the each device's configuration descriptors, and
supporting a series of ioctls for making device requests,
including I/O to devices. (Purely for access by programs.)
Each bus is given a number (BBB) based on when it was enumerated; within each bus, each device is given a similar number (DDD). Those BBB/DDD paths are not "stable" identifiers; expect them to change even if you always leave the devices plugged in to the same hub port. Don't even think of saving these in application configuration files. Stable identifiers are available, for user mode applications that want to use them. HID and networking devices expose these stable IDs, so that for example you can be sure that you told the right UPS to power down its second server. "usbfs" doesn't (yet) expose those IDs.
There are a number of mount options for usbfs, which will
be of most interest to you if you need to override the default
access control policy.
That policy is that only root may read or write device files
(/proc/bus/BBB/DDD) although anyone may read
the devices
or drivers files.
I/O requests to the device also need the CAP_SYS_RAWIO capability,
The significance of that is that by default, all user mode device drivers need super-user privileges. You can change modes or ownership in a driver setup when the device hotplugs, or maye just start the driver right then, as a privileged server (or some activity within one). That's the most secure approach for multi-user systems, but for single user systems ("trusted" by that user) it's more convenient just to grant everyone all access (using the devmode=0666 option) so the driver can start whenever it's needed.
The mount options for usbfs, usable in /etc/fstab or in command line invocations of mount, are:
Controls the GID used for the /proc/bus/usb/BBB directories. (Default: 0)
Controls the file mode used for the /proc/bus/usb/BBB directories. (Default: 0555)
Controls the UID used for the /proc/bus/usb/BBB directories. (Default: 0)
Controls the GID used for the /proc/bus/usb/BBB/DDD files. (Default: 0)
Controls the file mode used for the /proc/bus/usb/BBB/DDD files. (Default: 0644)
Controls the UID used for the /proc/bus/usb/BBB/DDD files. (Default: 0)
Controls the GID used for the /proc/bus/usb/devices and drivers files. (Default: 0)
Controls the file mode used for the /proc/bus/usb/devices and drivers files. (Default: 0444)
Controls the UID used for the /proc/bus/usb/devices and drivers files. (Default: 0)
Note that many Linux distributions hard-wire the mount options
for usbfs in their init scripts, such as
/etc/rc.d/rc.sysinit,
rather than making it easy to set this per-system
policy in /etc/fstab.
This file is handy for status viewing tools in user
mode, which can scan the text format and ignore most of it.
More detailed device status (including class and vendor
status) is available from device-specific files.
For information about the current format of this file,
see the
Documentation/usb/proc_usb_info.txt
file in your Linux kernel sources.
This file, in combination with the poll() system call, can also be used to detect when devices are added or removed:
int fd;
struct pollfd pfd;
fd = open("/proc/bus/usb/devices", O_RDONLY);
pfd = { fd, POLLIN, 0 };
for (;;) {
/* The first time through, this call will return immediately. */
poll(&pfd, 1, -1);
/* To see what's changed, compare the file's previous and current
contents or scan the filesystem. (Scanning is more precise.) */
}Note that this behavior is intended to be used for informational and debug purposes. It would be more appropriate to use programs such as udev or HAL to initialize a device or start a user-mode helper program, for instance.
Use these files in one of these basic ways:
They can be read, producing first the device descriptor (18 bytes) and then the descriptors for the current configuration. See the USB 2.0 spec for details about those binary data formats. You'll need to convert most multibyte values from little endian format to your native host byte order, although a few of the fields in the device descriptor (both of the BCD-encoded fields, and the vendor and product IDs) will be byteswapped for you. Note that configuration descriptors include descriptors for interfaces, altsettings, endpoints, and maybe additional class descriptors.
Perform USB operations using ioctl() requests to make endpoint I/O requests (synchronously or asynchronously) or manage the device. These requests need the CAP_SYS_RAWIO capability, as well as filesystem access permissions. Only one ioctl request can be made on one of these device files at a time. This means that if you are synchronously reading an endpoint from one thread, you won't be able to write to a different endpoint from another thread until the read completes. This works for half duplex protocols, but otherwise you'd use asynchronous i/o requests.
Such a driver first needs to find a device file
for a device it knows how to handle.
Maybe it was told about it because a
/sbin/hotplug event handling agent
chose that driver to handle the new device.
Or maybe it's an application that scans all the
/proc/bus/usb device files, and ignores most devices.
In either case, it should read() all
the descriptors from the device file,
and check them against what it knows how to handle.
It might just reject everything except a particular
vendor and product ID, or need a more complex policy.
Never assume there will only be one such device on the system at a time! If your code can't handle more than one device at a time, at least detect when there's more than one, and have your users choose which device to use.
Once your user mode driver knows what device to use, it interacts with it in either of two styles. The simple style is to make only control requests; some devices don't need more complex interactions than those. (An example might be software using vendor-specific control requests for some initialization or configuration tasks, with a kernel driver for the rest.)
More likely, you need a more complex style driver: one using non-control endpoints, reading or writing data and claiming exclusive use of an interface. Bulk transfers are easiest to use, but only their sibling interrupt transfers work with low speed devices. Both interrupt and isochronous transfers offer service guarantees because their bandwidth is reserved. Such "periodic" transfers are awkward to use through usbfs, unless you're using the asynchronous calls. However, interrupt transfers can also be used in a synchronous "one shot" style.
Your user-mode driver should never need to worry about cleaning up request state when the device is disconnected, although it should close its open file descriptors as soon as it starts seeing the ENODEV errors.
To use these ioctls, you need to include the following headers in your userspace program:
#include <linux/usb.h> #include <linux/usbdevice_fs.h> #include <asm/byteorder.h>
The standard USB device model requests, from "Chapter 9" of
the USB 2.0 specification, are automatically included from
the <linux/usb/ch9.h> header.
Unless noted otherwise, the ioctl requests
described here will
update the modification time on the usbfs file to which
they are applied (unless they fail).
A return of zero indicates success; otherwise, a
standard USB error code is returned. (These are
documented in
Documentation/usb/error-codes.txt
in your kernel sources.)
Each of these files multiplexes access to several I/O streams, one per endpoint. Each device has one control endpoint (endpoint zero) which supports a limited RPC style RPC access. Devices are configured by khubd (in the kernel) setting a device-wide configuration that affects things like power consumption and basic functionality. The endpoints are part of USB interfaces, which may have altsettings affecting things like which endpoints are available. Many devices only have a single configuration and interface, so drivers for them will ignore configurations and altsettings.
A number of usbfs requests don't deal very directly with device I/O. They mostly relate to device management and status. These are all synchronous requests.
This is used to force usbfs to claim a specific interface, which has not previously been claimed by usbfs or any other kernel driver. The ioctl parameter is an integer holding the number of the interface (bInterfaceNumber from descriptor).
Note that if your driver doesn't claim an interface before trying to use one of its endpoints, and no other driver has bound to it, then the interface is automatically claimed by usbfs.
This claim will be released by a RELEASEINTERFACE ioctl, or by closing the file descriptor. File modification time is not updated by this request.
Says whether the device is lowspeed. The ioctl parameter points to a structure like this:
struct usbdevfs_connectinfo {
unsigned int devnum;
unsigned char slow;
}; File modification time is not updated by this request.
You can't tell whether a "not slow" device is connected at high speed (480 MBit/sec) or just full speed (12 MBit/sec). You should know the devnum value already, it's the DDD value of the device file name.
Returns the name of the kernel driver bound to a given interface (a string). Parameter is a pointer to this structure, which is modified:
struct usbdevfs_getdriver {
unsigned int interface;
char driver[USBDEVFS_MAXDRIVERNAME + 1];
};File modification time is not updated by this request.
Passes a request from userspace through to a kernel driver that has an ioctl entry in the struct usb_driver it registered.
struct usbdevfs_ioctl {
int ifno;
int ioctl_code;
void *data;
};
/* user mode call looks like this.
* 'request' becomes the driver->ioctl() 'code' parameter.
* the size of 'param' is encoded in 'request', and that data
* is copied to or from the driver->ioctl() 'buf' parameter.
*/
static int
usbdev_ioctl (int fd, int ifno, unsigned request, void *param)
{
struct usbdevfs_ioctl wrapper;
wrapper.ifno = ifno;
wrapper.ioctl_code = request;
wrapper.data = param;
return ioctl (fd, USBDEVFS_IOCTL, &wrapper);
} File modification time is not updated by this request.
This request lets kernel drivers talk to user mode code through filesystem operations even when they don't create a charactor or block special device. It's also been used to do things like ask devices what device special file should be used. Two pre-defined ioctls are used to disconnect and reconnect kernel drivers, so that user mode code can completely manage binding and configuration of devices.
This is used to release the claim usbfs made on interface, either implicitly or because of a USBDEVFS_CLAIMINTERFACE call, before the file descriptor is closed. The ioctl parameter is an integer holding the number of the interface (bInterfaceNumber from descriptor); File modification time is not updated by this request.
No security check is made to ensure that the task which made the claim is the one which is releasing it. This means that user mode driver may interfere other ones.
Resets the data toggle value for an endpoint (bulk or interrupt) to DATA0. The ioctl parameter is an integer endpoint number (1 to 15, as identified in the endpoint descriptor), with USB_DIR_IN added if the device's endpoint sends data to the host.
Avoid using this request. It should probably be removed. Using it typically means the device and driver will lose toggle synchronization. If you really lost synchronization, you likely need to completely handshake with the device, using a request like CLEAR_HALT or SET_INTERFACE.
Synchronous requests involve the kernel blocking until the user mode request completes, either by finishing successfully or by reporting an error. In most cases this is the simplest way to use usbfs, although as noted above it does prevent performing I/O to more than one endpoint at a time.
Issues a bulk read or write request to the device. The ioctl parameter is a pointer to this structure:
struct usbdevfs_bulktransfer {
unsigned int ep;
unsigned int len;
unsigned int timeout; /* in milliseconds */
void *data;
};
The "ep" value identifies a bulk endpoint number (1 to 15, as identified in an endpoint descriptor), masked with USB_DIR_IN when referring to an endpoint which sends data to the host from the device. The length of the data buffer is identified by "len"; Recent kernels support requests up to about 128KBytes. FIXME say how read length is returned, and how short reads are handled..
Clears endpoint halt (stall) and resets the endpoint toggle. This is only meaningful for bulk or interrupt endpoints. The ioctl parameter is an integer endpoint number (1 to 15, as identified in an endpoint descriptor), masked with USB_DIR_IN when referring to an endpoint which sends data to the host from the device.
Use this on bulk or interrupt endpoints which have stalled, returning -EPIPE status to a data transfer request. Do not issue the control request directly, since that could invalidate the host's record of the data toggle.
Issues a control request to the device. The ioctl parameter points to a structure like this:
struct usbdevfs_ctrltransfer {
__u8 bRequestType;
__u8 bRequest;
__u16 wValue;
__u16 wIndex;
__u16 wLength;
__u32 timeout; /* in milliseconds */
void *data;
};
The first eight bytes of this structure are the contents of the SETUP packet to be sent to the device; see the USB 2.0 specification for details. The bRequestType value is composed by combining a USB_TYPE_* value, a USB_DIR_* value, and a USB_RECIP_* value (from <linux/usb.h>). If wLength is nonzero, it describes the length of the data buffer, which is either written to the device (USB_DIR_OUT) or read from the device (USB_DIR_IN).
At this writing, you can't transfer more than 4 KBytes of data to or from a device; usbfs has a limit, and some host controller drivers have a limit. (That's not usually a problem.) Also there's no way to say it's not OK to get a short read back from the device.
Does a USB level device reset. The ioctl parameter is ignored. After the reset, this rebinds all device interfaces. File modification time is not updated by this request.
Avoid using this call until some usbcore bugs get fixed, since it does not fully synchronize device, interface, and driver (not just usbfs) state.
Sets the alternate setting for an interface. The ioctl parameter is a pointer to a structure like this:
struct usbdevfs_setinterface {
unsigned int interface;
unsigned int altsetting;
}; File modification time is not updated by this request.
Those struct members are from some interface descriptor applying to the current configuration. The interface number is the bInterfaceNumber value, and the altsetting number is the bAlternateSetting value. (This resets each endpoint in the interface.)
Issues the
usb_set_configuration call
for the device.
The parameter is an integer holding the number of
a configuration (bConfigurationValue from descriptor).
File modification time is not updated by this request.
Avoid using this call until some usbcore bugs get fixed, since it does not fully synchronize device, interface, and driver (not just usbfs) state.
As mentioned above, there are situations where it may be important to initiate concurrent operations from user mode code. This is particularly important for periodic transfers (interrupt and isochronous), but it can be used for other kinds of USB requests too. In such cases, the asynchronous requests described here are essential. Rather than submitting one request and having the kernel block until it completes, the blocking is separate.
These requests are packaged into a structure that resembles the URB used by kernel device drivers. (No POSIX Async I/O support here, sorry.) It identifies the endpoint type (USBDEVFS_URB_TYPE_*), endpoint (number, masked with USB_DIR_IN as appropriate), buffer and length, and a user "context" value serving to uniquely identify each request. (It's usually a pointer to per-request data.) Flags can modify requests (not as many as supported for kernel drivers).
Each request can specify a realtime signal number (between SIGRTMIN and SIGRTMAX, inclusive) to request a signal be sent when the request completes.
When usbfs returns these urbs, the status value is updated, and the buffer may have been modified. Except for isochronous transfers, the actual_length is updated to say how many bytes were transferred; if the USBDEVFS_URB_DISABLE_SPD flag is set ("short packets are not OK"), if fewer bytes were read than were requested then you get an error report.
struct usbdevfs_iso_packet_desc {
unsigned int length;
unsigned int actual_length;
unsigned int status;
};
struct usbdevfs_urb {
unsigned char type;
unsigned char endpoint;
int status;
unsigned int flags;
void *buffer;
int buffer_length;
int actual_length;
int start_frame;
int number_of_packets;
int error_count;
unsigned int signr;
void *usercontext;
struct usbdevfs_iso_packet_desc iso_frame_desc[];
};For these asynchronous requests, the file modification time reflects when the request was initiated. This contrasts with their use with the synchronous requests, where it reflects when requests complete.
TBS File modification time is not updated by this request.
TBS File modification time is not updated by this request.
TBS File modification time is not updated by this request.
TBS File modification time is not updated by this request.
TBS