docs: move parisc documentation under Documentation/arch/

Architecture-specific documentation is being moved into Documentation/arch/
as a way of cleaning up the top-level documentation directory and making
the docs hierarchy more closely match the source hierarchy.  Move
Documentation/parisc into arch/ and fix all in-tree references.

Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Alex Shi <alexs@kernel.org>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

5 files changed, 224 insertions, 1 deletions

diff --git a/Documentation/arch/index.rst b/Documentation/arch/index.rst
index 77e287c3eeb9b7..6839cd46850d47 100644
--- a/Documentation/arch/index.rst
+++ b/Documentation/arch/index.rst
@@ -18,7 +18,7 @@ implementation.
    ../mips/index
    nios2/index
    openrisc/index
-   ../parisc/index
+   parisc/index
    ../powerpc/index
    ../riscv/index
    ../s390/index
diff --git a/Documentation/arch/parisc/debugging.rst b/Documentation/arch/parisc/debugging.rst
new file mode 100644
index 00000000000000..de1b60402c5b89
--- /dev/null
+++ b/Documentation/arch/parisc/debugging.rst
@@ -0,0 +1,46 @@
+=================
+PA-RISC Debugging
+=================
+
+okay, here are some hints for debugging the lower-level parts of
+linux/parisc.
+
+
+1. Absolute addresses
+=====================
+
+A lot of the assembly code currently runs in real mode, which means
+absolute addresses are used instead of virtual addresses as in the
+rest of the kernel.  To translate an absolute address to a virtual
+address you can lookup in System.map, add __PAGE_OFFSET (0x10000000
+currently).
+
+
+2. HPMCs
+========
+
+When real-mode code tries to access non-existent memory, you'll get
+an HPMC instead of a kernel oops.  To debug an HPMC, try to find
+the System Responder/Requestor addresses.  The System Requestor
+address should match (one of the) processor HPAs (high addresses in
+the I/O range); the System Responder address is the address real-mode
+code tried to access.
+
+Typical values for the System Responder address are addresses larger
+than __PAGE_OFFSET (0x10000000) which mean a virtual address didn't
+get translated to a physical address before real-mode code tried to
+access it.
+
+
+3. Q bit fun
+============
+
+Certain, very critical code has to clear the Q bit in the PSW.  What
+happens when the Q bit is cleared is the CPU does not update the
+registers interruption handlers read to find out where the machine
+was interrupted - so if you get an interruption between the instruction
+that clears the Q bit and the RFI that sets it again you don't know
+where exactly it happened.  If you're lucky the IAOQ will point to the
+instruction that cleared the Q bit, if you're not it points anywhere
+at all.  Usually Q bit problems will show themselves in unexplainable
+system hangs or running off the end of physical memory.
diff --git a/Documentation/arch/parisc/features.rst b/Documentation/arch/parisc/features.rst
new file mode 100644
index 00000000000000..501d7c45003790
--- /dev/null
+++ b/Documentation/arch/parisc/features.rst
@@ -0,0 +1,3 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. kernel-feat:: $srctree/Documentation/features parisc
diff --git a/Documentation/arch/parisc/index.rst b/Documentation/arch/parisc/index.rst
new file mode 100644
index 00000000000000..24068575182527
--- /dev/null
+++ b/Documentation/arch/parisc/index.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+====================
+PA-RISC Architecture
+====================
+
+.. toctree::
+   :maxdepth: 2
+
+   debugging
+   registers
+
+   features
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`
diff --git a/Documentation/arch/parisc/registers.rst b/Documentation/arch/parisc/registers.rst
new file mode 100644
index 00000000000000..59c8ecf3e856ae
--- /dev/null
+++ b/Documentation/arch/parisc/registers.rst
@@ -0,0 +1,154 @@
+================================
+Register Usage for Linux/PA-RISC
+================================
+
+[ an asterisk is used for planned usage which is currently unimplemented ]
+
+General Registers as specified by ABI
+=====================================
+
+Control Registers
+-----------------
+
+===============================	===============================================
+CR 0 (Recovery Counter)		used for ptrace
+CR 1-CR 7(undefined)		unused
+CR 8 (Protection ID)		per-process value*
+CR 9, 12, 13 (PIDS)		unused
+CR10 (CCR)			lazy FPU saving*
+CR11				as specified by ABI (SAR)
+CR14 (interruption vector)	initialized to fault_vector
+CR15 (EIEM)			initialized to all ones*
+CR16 (Interval Timer)		read for cycle count/write starts Interval Tmr
+CR17-CR22			interruption parameters
+CR19				Interrupt Instruction Register
+CR20				Interrupt Space Register
+CR21				Interrupt Offset Register
+CR22				Interrupt PSW
+CR23 (EIRR)			read for pending interrupts/write clears bits
+CR24 (TR 0)			Kernel Space Page Directory Pointer
+CR25 (TR 1)			User   Space Page Directory Pointer
+CR26 (TR 2)			not used
+CR27 (TR 3)			Thread descriptor pointer
+CR28 (TR 4)			not used
+CR29 (TR 5)			not used
+CR30 (TR 6)			current / 0
+CR31 (TR 7)			Temporary register, used in various places
+===============================	===============================================
+
+Space Registers (kernel mode)
+-----------------------------
+
+===============================	===============================================
+SR0				temporary space register
+SR4-SR7 			set to 0
+SR1				temporary space register
+SR2				kernel should not clobber this
+SR3				used for userspace accesses (current process)
+===============================	===============================================
+
+Space Registers (user mode)
+---------------------------
+
+===============================	===============================================
+SR0				temporary space register
+SR1                             temporary space register
+SR2                             holds space of linux gateway page
+SR3                             holds user address space value while in kernel
+SR4-SR7                         Defines short address space for user/kernel
+===============================	===============================================
+
+
+Processor Status Word
+---------------------
+
+===============================	===============================================
+W (64-bit addresses)		0
+E (Little-endian)		0
+S (Secure Interval Timer)	0
+T (Taken Branch Trap)		0
+H (Higher-privilege trap)	0
+L (Lower-privilege trap)	0
+N (Nullify next instruction)	used by C code
+X (Data memory break disable)	0
+B (Taken Branch)		used by C code
+C (code address translation)	1, 0 while executing real-mode code
+V (divide step correction)	used by C code
+M (HPMC mask)			0, 1 while executing HPMC handler*
+C/B (carry/borrow bits)		used by C code
+O (ordered references)		1*
+F (performance monitor)		0
+R (Recovery Counter trap)	0
+Q (collect interruption state)	1 (0 in code directly preceding an rfi)
+P (Protection Identifiers)	1*
+D (Data address translation)	1, 0 while executing real-mode code
+I (external interrupt mask)	used by cli()/sti() macros
+===============================	===============================================
+
+"Invisible" Registers
+---------------------
+
+===============================	===============================================
+PSW default W value		0
+PSW default E value		0
+Shadow Registers		used by interruption handler code
+TOC enable bit			1
+===============================	===============================================
+
+-------------------------------------------------------------------------
+
+The PA-RISC architecture defines 7 registers as "shadow registers".
+Those are used in RETURN FROM INTERRUPTION AND RESTORE instruction to reduce
+the state save and restore time by eliminating the need for general register
+(GR) saves and restores in interruption handlers.
+Shadow registers are the GRs 1, 8, 9, 16, 17, 24, and 25.
+
+-------------------------------------------------------------------------
+
+Register usage notes, originally from John Marvin, with some additional
+notes from Randolph Chung.
+
+For the general registers:
+
+r1,r2,r19-r26,r28,r29 & r31 can be used without saving them first. And of
+course, you need to save them if you care about them, before calling
+another procedure. Some of the above registers do have special meanings
+that you should be aware of:
+
+    r1:
+	The addil instruction is hardwired to place its result in r1,
+	so if you use that instruction be aware of that.
+
+    r2:
+	This is the return pointer. In general you don't want to
+	use this, since you need the pointer to get back to your
+	caller. However, it is grouped with this set of registers
+	since the caller can't rely on the value being the same
+	when you return, i.e. you can copy r2 to another register
+	and return through that register after trashing r2, and
+	that should not cause a problem for the calling routine.
+
+    r19-r22:
+	these are generally regarded as temporary registers.
+	Note that in 64 bit they are arg7-arg4.
+
+    r23-r26:
+	these are arg3-arg0, i.e. you can use them if you
+	don't care about the values that were passed in anymore.
+
+    r28,r29:
+	are ret0 and ret1. They are what you pass return values
+	in. r28 is the primary return. When returning small structures
+	r29 may also be used to pass data back to the caller.
+
+    r30:
+	stack pointer
+
+    r31:
+	the ble instruction puts the return pointer in here.
+
+
+    r3-r18,r27,r30 need to be saved and restored. r3-r18 are just
+    general purpose registers. r27 is the data pointer, and is
+    used to make references to global variables easier. r30 is
+    the stack pointer.