# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2 --- $id: http://devicetree.org/schemas/mailbox/arm,mhuv3.yaml# $schema: http://devicetree.org/meta-schemas/core.yaml# title: ARM MHUv3 Mailbox Controller maintainers: - Sudeep Holla - Cristian Marussi description: | The Arm Message Handling Unit (MHU) Version 3 is a mailbox controller that enables unidirectional communications with remote processors through various possible transport protocols. The controller can optionally support a varying number of extensions that, in turn, enable different kinds of transport to be used for communication. Number, type and characteristics of each supported extension can be discovered dynamically at runtime. Given the unidirectional nature of the controller, an MHUv3 mailbox controller is composed of a MHU Sender (MHUS) containing a PostBox (PBX) block and a MHU Receiver (MHUR) containing a MailBox (MBX) block, where PBX is used to - Configure the MHU - Send Transfers to the Receiver - Optionally receive acknowledgment of a Transfer from the Receiver MBX is used to - Configure the MHU - Receive Transfers from the Sender - Optionally acknowledge Transfers sent by the Sender Both PBX and MBX need to be present and defined in the DT description if you need to establish a bidirectional communication, since you will have to acquire two distinct unidirectional channels, one for each block. As a consequence both blocks needs to be represented separately and specified as distinct DT nodes in order to properly describe their resources. Note that, though, thanks to the runtime discoverability, there is no need to identify the type of blocks with distinct compatibles. Following are the MHUv3 possible extensions. - Doorbell Extension (DBE): DBE defines a type of channel called a Doorbell Channel (DBCH). DBCH enables a single bit Transfer to be sent from the Sender to Receiver. The Transfer indicates that an event has occurred. When DBE is implemented, the number of DBCHs that an implementation of the MHU can support is between 1 and 128, numbered starting from 0 in ascending order and discoverable at run-time. Each DBCH contains 32 individual fields, referred to as flags, each of which can be used independently. It is possible for the Sender to send multiple Transfers at once using a single DBCH, so long as each Transfer uses a different flag in the DBCH. Optionally, data may be transmitted through an out-of-band shared memory region, wherein the MHU Doorbell is used strictly as an interrupt generation mechanism, but this is out of the scope of these bindings. - FastChannel Extension (FCE): FCE defines a type of channel called a Fast Channel (FCH). FCH is intended for lower overhead communication between Sender and Receiver at the expense of determinism. An FCH allows the Sender to update the channel value at any time, regardless of whether the previous value has been seen by the Receiver. When the Receiver reads the channel's content it gets the last value written to the channel. FCH is considered lossy in nature, and means that the Sender has no way of knowing if, or when, the Receiver will act on the Transfer. FCHs are expected to behave as RAM which generates interrupts when writes occur to the locations within the RAM. When FCE is implemented, the number of FCHs that an implementation of the MHU can support is between 1-1024, if the FastChannel word-size is 32-bits, or between 1-512, when the FastChannel word-size is 64-bits. FCHs are numbered from 0 in ascending order. Note that the number of FCHs and the word-size are implementation defined, not configurable but discoverable at run-time. Optionally, data may be transmitted through an out-of-band shared memory region, wherein the MHU FastChannel is used as an interrupt generation mechanism which carries also a pointer to such out-of-band data, but this is out of the scope of these bindings. - FIFO Extension (FE): FE defines a Channel type called a FIFO Channel (FFCH). FFCH allows a Sender to send - Multiple Transfers to the Receiver without having to wait for the previous Transfer to be acknowledged by the Receiver, as long as the FIFO has room for the Transfer. - Transfers which require the Receiver to provide acknowledgment. - Transfers which have in-band payload. In all cases, the data is guaranteed to be observed by the Receiver in the same order which the Sender sent it. When FE is implemented, the number of FFCHs that an implementation of the MHU can support is between 1 and 64, numbered starting from 0 in ascending order. The number of FFCHs, their depth (same for all implemented FFCHs) and the access-granularity are implementation defined, not configurable but discoverable at run-time. Optionally, additional data may be transmitted through an out-of-band shared memory region, wherein the MHU FIFO is used to transmit, in order, a small part of the payload (like a header) and a reference to the shared memory area holding the remaining, bigger, chunk of the payload, but this is out of the scope of these bindings. properties: compatible: const: arm,mhuv3 reg: maxItems: 1 interrupts: minItems: 1 maxItems: 74 interrupt-names: description: | The MHUv3 controller generates a number of events some of which are used to generate interrupts; as a consequence it can expose a varying number of optional PBX/MBX interrupts, representing the events generated during the operation of the various transport protocols associated with different extensions. All interrupts of the MHU are level-sensitive. Some of these optional interrupts are defined per-channel, where the number of channels effectively available is implementation defined and run-time discoverable. In the following names are enumerated using patterns, with per-channel interrupts implicitly capped at the maximum channels allowed by the specification for each extension type. For the sake of simplicity maxItems is anyway capped to a most plausible number, assuming way less channels would be implemented than actually possible. The only mandatory interrupts on the MHU are: - combined - mbx-fch-xfer- but only if mbx-fcgrp-xfer- is not implemented. minItems: 1 maxItems: 74 items: oneOf: - const: combined description: PBX/MBX Combined interrupt - const: combined-ffch description: PBX/MBX FIFO Combined interrupt - pattern: '^ffch-low-tide-[0-9]+$' description: PBX/MBX FIFO Channel Low Tide interrupt - pattern: '^ffch-high-tide-[0-9]+$' description: PBX/MBX FIFO Channel High Tide interrupt - pattern: '^ffch-flush-[0-9]+$' description: PBX/MBX FIFO Channel Flush interrupt - pattern: '^mbx-dbch-xfer-[0-9]+$' description: MBX Doorbell Channel Transfer interrupt - pattern: '^mbx-fch-xfer-[0-9]+$' description: MBX FastChannel Transfer interrupt - pattern: '^mbx-fchgrp-xfer-[0-9]+$' description: MBX FastChannel Group Transfer interrupt - pattern: '^mbx-ffch-xfer-[0-9]+$' description: MBX FIFO Channel Transfer interrupt - pattern: '^pbx-dbch-xfer-ack-[0-9]+$' description: PBX Doorbell Channel Transfer Ack interrupt - pattern: '^pbx-ffch-xfer-ack-[0-9]+$' description: PBX FIFO Channel Transfer Ack interrupt '#mbox-cells': description: | The first argument in the consumers 'mboxes' property represents the extension type, the second is for the channel number while the third depends on extension type. Extension types constants are defined in . Extension type for DBE is DBE_EXT and the third parameter represents the doorbell flag number to use. Extension type for FCE is FCE_EXT, third parameter unused. Extension type for FE is FE_EXT, third parameter unused. mboxes = <&mhu DBE_EXT 0 5>; // DBE, Doorbell Channel Window 0, doorbell 5. mboxes = <&mhu DBE_EXT 7>; // DBE, Doorbell Channel Window 1, doorbell 7. mboxes = <&mhu FCE_EXT 0 0>; // FCE, FastChannel Window 0. mboxes = <&mhu FCE_EXT 3 0>; // FCE, FastChannel Window 3. mboxes = <&mhu FE_EXT 1 0>; // FE, FIFO Channel Window 1. mboxes = <&mhu FE_EXT 7 0>; // FE, FIFO Channel Window 7. const: 3 clocks: maxItems: 1 required: - compatible - reg - interrupts - interrupt-names - '#mbox-cells' additionalProperties: false examples: - | #include soc { #address-cells = <2>; #size-cells = <2>; mailbox@2aaa0000 { compatible = "arm,mhuv3"; #mbox-cells = <3>; reg = <0 0x2aaa0000 0 0x10000>; clocks = <&clock 0>; interrupt-names = "combined", "pbx-dbch-xfer-ack-1", "ffch-high-tide-0"; interrupts = , ; }; mailbox@2ab00000 { compatible = "arm,mhuv3"; #mbox-cells = <3>; reg = <0 0x2aab0000 0 0x10000>; clocks = <&clock 0>; interrupt-names = "combined", "mbx-dbch-xfer-1", "ffch-low-tide-0"; interrupts = , , ; }; };