Merge tag 'docs-6.6' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "Documentation work keeps chugging along; this includes:

   - Work from Carlos Bilbao to integrate rustdoc output into the
     generated HTML documentation. This took some work to figure out how
     to do it without slowing the docs build and without creating people
     who don't have Rust installed, but Carlos got there

   - Move the loongarch and mips architecture documentation under
     Documentation/arch/

   - Some more maintainer documentation from Jakub

  ... plus the usual assortment of updates, translations, and fixes"

* tag 'docs-6.6' of git://git.lwn.net/linux: (56 commits)
  Docu: genericirq.rst: fix irq-example
  input: docs: pxrc: remove reference to phoenix-sim
  Documentation: serial-console: Fix literal block marker
  docs/mm: remove references to hmm_mirror ops and clean typos
  docs/zh_CN: correct regi_chg(),regi_add() to region_chg(),region_add()
  Documentation: Fix typos
  Documentation/ABI: Fix typos
  scripts: kernel-doc: fix macro handling in enums
  scripts: kernel-doc: parse DEFINE_DMA_UNMAP_[ADDR|LEN]
  Documentation: riscv: Update boot image header since EFI stub is supported
  Documentation: riscv: Add early boot document
  Documentation: arm: Add bootargs to the table of added DT parameters
  docs: kernel-parameters: Refer to the correct bitmap function
  doc: update params of memhp_default_state=
  docs: Add book to process/kernel-docs.rst
  docs: sparse: fix invalid link addresses
  docs: vfs: clean up after the iterate() removal
  docs: Add a section on surveys to the researcher guidelines
  docs: move mips under arch
  docs: move loongarch under arch
  ...

5 files changed, 617 insertions, 0 deletions

diff --git a/Documentation/arch/loongarch/booting.rst b/Documentation/arch/loongarch/booting.rst
new file mode 100644
index 000000000000..91eccd410478
--- /dev/null
+++ b/Documentation/arch/loongarch/booting.rst
@@ -0,0 +1,42 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+Booting Linux/LoongArch
+=======================
+
+:Author: Yanteng Si <siyanteng@loongson.cn>
+:Date:   18 Nov 2022
+
+Information passed from BootLoader to kernel
+============================================
+
+LoongArch supports ACPI and FDT. The information that needs to be passed
+to the kernel includes the memmap, the initrd, the command line, optionally
+the ACPI/FDT tables, and so on.
+
+The kernel is passed the following arguments on `kernel_entry` :
+
+      - a0 = efi_boot: `efi_boot` is a flag indicating whether
+        this boot environment is fully UEFI-compliant.
+
+      - a1 = cmdline: `cmdline` is a pointer to the kernel command line.
+
+      - a2 = systemtable: `systemtable` points to the EFI system table.
+        All pointers involved at this stage are in physical addresses.
+
+Header of Linux/LoongArch kernel images
+=======================================
+
+Linux/LoongArch kernel images are EFI images. Being PE files, they have
+a 64-byte header structured like::
+
+	u32	MZ_MAGIC                /* "MZ", MS-DOS header */
+	u32	res0 = 0                /* Reserved */
+	u64	kernel_entry            /* Kernel entry point */
+	u64	_end - _text            /* Kernel image effective size */
+	u64	load_offset             /* Kernel image load offset from start of RAM */
+	u64	res1 = 0                /* Reserved */
+	u64	res2 = 0                /* Reserved */
+	u64	res3 = 0                /* Reserved */
+	u32	LINUX_PE_MAGIC          /* Magic number */
+	u32	pe_header - _head       /* Offset to the PE header */
diff --git a/Documentation/arch/loongarch/features.rst b/Documentation/arch/loongarch/features.rst
new file mode 100644
index 000000000000..ebacade3ea45
--- /dev/null
+++ b/Documentation/arch/loongarch/features.rst
@@ -0,0 +1,3 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. kernel-feat:: $srctree/Documentation/features loongarch
diff --git a/Documentation/arch/loongarch/index.rst b/Documentation/arch/loongarch/index.rst
new file mode 100644
index 000000000000..c779bfa00c05
--- /dev/null
+++ b/Documentation/arch/loongarch/index.rst
@@ -0,0 +1,22 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======================
+LoongArch Architecture
+======================
+
+.. toctree::
+   :maxdepth: 2
+   :numbered:
+
+   introduction
+   booting
+   irq-chip-model
+
+   features
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`
diff --git a/Documentation/arch/loongarch/introduction.rst b/Documentation/arch/loongarch/introduction.rst
new file mode 100644
index 000000000000..49135d451ced
--- /dev/null
+++ b/Documentation/arch/loongarch/introduction.rst
@@ -0,0 +1,390 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+Introduction to LoongArch
+=========================
+
+LoongArch is a new RISC ISA, which is a bit like MIPS or RISC-V. There are
+currently 3 variants: a reduced 32-bit version (LA32R), a standard 32-bit
+version (LA32S) and a 64-bit version (LA64). There are 4 privilege levels
+(PLVs) defined in LoongArch: PLV0~PLV3, from high to low. Kernel runs at PLV0
+while applications run at PLV3. This document introduces the registers, basic
+instruction set, virtual memory and some other topics of LoongArch.
+
+Registers
+=========
+
+LoongArch registers include general purpose registers (GPRs), floating point
+registers (FPRs), vector registers (VRs) and control status registers (CSRs)
+used in privileged mode (PLV0).
+
+GPRs
+----
+
+LoongArch has 32 GPRs ( ``$r0`` ~ ``$r31`` ); each one is 32-bit wide in LA32
+and 64-bit wide in LA64. ``$r0`` is hard-wired to zero, and the other registers
+are not architecturally special. (Except ``$r1``, which is hard-wired as the
+link register of the BL instruction.)
+
+The kernel uses a variant of the LoongArch register convention, as described in
+the LoongArch ELF psABI spec, in :ref:`References <loongarch-references>`:
+
+================= =============== =================== ============
+Name              Alias           Usage               Preserved
+                                                      across calls
+================= =============== =================== ============
+``$r0``           ``$zero``       Constant zero       Unused
+``$r1``           ``$ra``         Return address      No
+``$r2``           ``$tp``         TLS/Thread pointer  Unused
+``$r3``           ``$sp``         Stack pointer       Yes
+``$r4``-``$r11``  ``$a0``-``$a7`` Argument registers  No
+``$r4``-``$r5``   ``$v0``-``$v1`` Return value        No
+``$r12``-``$r20`` ``$t0``-``$t8`` Temp registers      No
+``$r21``          ``$u0``         Percpu base address Unused
+``$r22``          ``$fp``         Frame pointer       Yes
+``$r23``-``$r31`` ``$s0``-``$s8`` Static registers    Yes
+================= =============== =================== ============
+
+.. Note::
+    The register ``$r21`` is reserved in the ELF psABI, but used by the Linux
+    kernel for storing the percpu base address. It normally has no ABI name,
+    but is called ``$u0`` in the kernel. You may also see ``$v0`` or ``$v1``
+    in some old code,however they are deprecated aliases of ``$a0`` and ``$a1``
+    respectively.
+
+FPRs
+----
+
+LoongArch has 32 FPRs ( ``$f0`` ~ ``$f31`` ) when FPU is present. Each one is
+64-bit wide on the LA64 cores.
+
+The floating-point register convention is the same as described in the
+LoongArch ELF psABI spec:
+
+================= ================== =================== ============
+Name              Alias              Usage               Preserved
+                                                         across calls
+================= ================== =================== ============
+``$f0``-``$f7``   ``$fa0``-``$fa7``  Argument registers  No
+``$f0``-``$f1``   ``$fv0``-``$fv1``  Return value        No
+``$f8``-``$f23``  ``$ft0``-``$ft15`` Temp registers      No
+``$f24``-``$f31`` ``$fs0``-``$fs7``  Static registers    Yes
+================= ================== =================== ============
+
+.. Note::
+    You may see ``$fv0`` or ``$fv1`` in some old code, however they are
+    deprecated aliases of ``$fa0`` and ``$fa1`` respectively.
+
+VRs
+----
+
+There are currently 2 vector extensions to LoongArch:
+
+- LSX (Loongson SIMD eXtension) with 128-bit vectors,
+- LASX (Loongson Advanced SIMD eXtension) with 256-bit vectors.
+
+LSX brings ``$v0`` ~ ``$v31`` while LASX brings ``$x0`` ~ ``$x31`` as the vector
+registers.
+
+The VRs overlap with FPRs: for example, on a core implementing LSX and LASX,
+the lower 128 bits of ``$x0`` is shared with ``$v0``, and the lower 64 bits of
+``$v0`` is shared with ``$f0``; same with all other VRs.
+
+CSRs
+----
+
+CSRs can only be accessed from privileged mode (PLV0):
+
+================= ===================================== ==============
+Address           Full Name                             Abbrev Name
+================= ===================================== ==============
+0x0               Current Mode Information              CRMD
+0x1               Pre-exception Mode Information        PRMD
+0x2               Extension Unit Enable                 EUEN
+0x3               Miscellaneous Control                 MISC
+0x4               Exception Configuration               ECFG
+0x5               Exception Status                      ESTAT
+0x6               Exception Return Address              ERA
+0x7               Bad (Faulting) Virtual Address        BADV
+0x8               Bad (Faulting) Instruction Word       BADI
+0xC               Exception Entrypoint Address          EENTRY
+0x10              TLB Index                             TLBIDX
+0x11              TLB Entry High-order Bits             TLBEHI
+0x12              TLB Entry Low-order Bits 0            TLBELO0
+0x13              TLB Entry Low-order Bits 1            TLBELO1
+0x18              Address Space Identifier              ASID
+0x19              Page Global Directory Address for     PGDL
+                  Lower-half Address Space
+0x1A              Page Global Directory Address for     PGDH
+                  Higher-half Address Space
+0x1B              Page Global Directory Address         PGD
+0x1C              Page Walk Control for Lower-          PWCL
+                  half Address Space
+0x1D              Page Walk Control for Higher-         PWCH
+                  half Address Space
+0x1E              STLB Page Size                        STLBPS
+0x1F              Reduced Virtual Address Configuration RVACFG
+0x20              CPU Identifier                        CPUID
+0x21              Privileged Resource Configuration 1   PRCFG1
+0x22              Privileged Resource Configuration 2   PRCFG2
+0x23              Privileged Resource Configuration 3   PRCFG3
+0x30+n (0≤n≤15)   Saved Data register                   SAVEn
+0x40              Timer Identifier                      TID
+0x41              Timer Configuration                   TCFG
+0x42              Timer Value                           TVAL
+0x43              Compensation of Timer Count           CNTC
+0x44              Timer Interrupt Clearing              TICLR
+0x60              LLBit Control                         LLBCTL
+0x80              Implementation-specific Control 1     IMPCTL1
+0x81              Implementation-specific Control 2     IMPCTL2
+0x88              TLB Refill Exception Entrypoint       TLBRENTRY
+                  Address
+0x89              TLB Refill Exception BAD (Faulting)   TLBRBADV
+                  Virtual Address
+0x8A              TLB Refill Exception Return Address   TLBRERA
+0x8B              TLB Refill Exception Saved Data       TLBRSAVE
+                  Register
+0x8C              TLB Refill Exception Entry Low-order  TLBRELO0
+                  Bits 0
+0x8D              TLB Refill Exception Entry Low-order  TLBRELO1
+                  Bits 1
+0x8E              TLB Refill Exception Entry High-order TLBEHI
+                  Bits
+0x8F              TLB Refill Exception Pre-exception    TLBRPRMD
+                  Mode Information
+0x90              Machine Error Control                 MERRCTL
+0x91              Machine Error Information 1           MERRINFO1
+0x92              Machine Error Information 2           MERRINFO2
+0x93              Machine Error Exception Entrypoint    MERRENTRY
+                  Address
+0x94              Machine Error Exception Return        MERRERA
+                  Address
+0x95              Machine Error Exception Saved Data    MERRSAVE
+                  Register
+0x98              Cache TAGs                            CTAG
+0x180+n (0≤n≤3)   Direct Mapping Configuration Window n DMWn
+0x200+2n (0≤n≤31) Performance Monitor Configuration n   PMCFGn
+0x201+2n (0≤n≤31) Performance Monitor Overall Counter n PMCNTn
+0x300             Memory Load/Store WatchPoint          MWPC
+                  Overall Control
+0x301             Memory Load/Store WatchPoint          MWPS
+                  Overall Status
+0x310+8n (0≤n≤7)  Memory Load/Store WatchPoint n        MWPnCFG1
+                  Configuration 1
+0x311+8n (0≤n≤7)  Memory Load/Store WatchPoint n        MWPnCFG2
+                  Configuration 2
+0x312+8n (0≤n≤7)  Memory Load/Store WatchPoint n        MWPnCFG3
+                  Configuration 3
+0x313+8n (0≤n≤7)  Memory Load/Store WatchPoint n        MWPnCFG4
+                  Configuration 4
+0x380             Instruction Fetch WatchPoint          FWPC
+                  Overall Control
+0x381             Instruction Fetch WatchPoint          FWPS
+                  Overall Status
+0x390+8n (0≤n≤7)  Instruction Fetch WatchPoint n        FWPnCFG1
+                  Configuration 1
+0x391+8n (0≤n≤7)  Instruction Fetch WatchPoint n        FWPnCFG2
+                  Configuration 2
+0x392+8n (0≤n≤7)  Instruction Fetch WatchPoint n        FWPnCFG3
+                  Configuration 3
+0x393+8n (0≤n≤7)  Instruction Fetch WatchPoint n        FWPnCFG4
+                  Configuration 4
+0x500             Debug Register                        DBG
+0x501             Debug Exception Return Address        DERA
+0x502             Debug Exception Saved Data Register   DSAVE
+================= ===================================== ==============
+
+ERA, TLBRERA, MERRERA and DERA are sometimes also known as EPC, TLBREPC, MERREPC
+and DEPC respectively.
+
+Basic Instruction Set
+=====================
+
+Instruction formats
+-------------------
+
+LoongArch instructions are 32 bits wide, belonging to 9 basic instruction
+formats (and variants of them):
+
+=========== ==========================
+Format name Composition
+=========== ==========================
+2R          Opcode + Rj + Rd
+3R          Opcode + Rk + Rj + Rd
+4R          Opcode + Ra + Rk + Rj + Rd
+2RI8        Opcode + I8 + Rj + Rd
+2RI12       Opcode + I12 + Rj + Rd
+2RI14       Opcode + I14 + Rj + Rd
+2RI16       Opcode + I16 + Rj + Rd
+1RI21       Opcode + I21L + Rj + I21H
+I26         Opcode + I26L + I26H
+=========== ==========================
+
+Rd is the destination register operand, while Rj, Rk and Ra ("a" stands for
+"additional") are the source register operands. I8/I12/I14/I16/I21/I26 are
+immediate operands of respective width. The longer I21 and I26 are stored
+in separate higher and lower parts in the instruction word, denoted by the "L"
+and "H" suffixes.
+
+List of Instructions
+--------------------
+
+For brevity, only instruction names (mnemonics) are listed here; please see the
+:ref:`References <loongarch-references>` for details.
+
+
+1. Arithmetic Instructions::
+
+    ADD.W SUB.W ADDI.W ADD.D SUB.D ADDI.D
+    SLT SLTU SLTI SLTUI
+    AND OR NOR XOR ANDN ORN ANDI ORI XORI
+    MUL.W MULH.W MULH.WU DIV.W DIV.WU MOD.W MOD.WU
+    MUL.D MULH.D MULH.DU DIV.D DIV.DU MOD.D MOD.DU
+    PCADDI PCADDU12I PCADDU18I
+    LU12I.W LU32I.D LU52I.D ADDU16I.D
+
+2. Bit-shift Instructions::
+
+    SLL.W SRL.W SRA.W ROTR.W SLLI.W SRLI.W SRAI.W ROTRI.W
+    SLL.D SRL.D SRA.D ROTR.D SLLI.D SRLI.D SRAI.D ROTRI.D
+
+3. Bit-manipulation Instructions::
+
+    EXT.W.B EXT.W.H CLO.W CLO.D SLZ.W CLZ.D CTO.W CTO.D CTZ.W CTZ.D
+    BYTEPICK.W BYTEPICK.D BSTRINS.W BSTRINS.D BSTRPICK.W BSTRPICK.D
+    REVB.2H REVB.4H REVB.2W REVB.D REVH.2W REVH.D BITREV.4B BITREV.8B BITREV.W BITREV.D
+    MASKEQZ MASKNEZ
+
+4. Branch Instructions::
+
+    BEQ BNE BLT BGE BLTU BGEU BEQZ BNEZ B BL JIRL
+
+5. Load/Store Instructions::
+
+    LD.B LD.BU LD.H LD.HU LD.W LD.WU LD.D ST.B ST.H ST.W ST.D
+    LDX.B LDX.BU LDX.H LDX.HU LDX.W LDX.WU LDX.D STX.B STX.H STX.W STX.D
+    LDPTR.W LDPTR.D STPTR.W STPTR.D
+    PRELD PRELDX
+
+6. Atomic Operation Instructions::
+
+    LL.W SC.W LL.D SC.D
+    AMSWAP.W AMSWAP.D AMADD.W AMADD.D AMAND.W AMAND.D AMOR.W AMOR.D AMXOR.W AMXOR.D
+    AMMAX.W AMMAX.D AMMIN.W AMMIN.D
+
+7. Barrier Instructions::
+
+    IBAR DBAR
+
+8. Special Instructions::
+
+    SYSCALL BREAK CPUCFG NOP IDLE ERTN(ERET) DBCL(DBGCALL) RDTIMEL.W RDTIMEH.W RDTIME.D
+    ASRTLE.D ASRTGT.D
+
+9. Privileged Instructions::
+
+    CSRRD CSRWR CSRXCHG
+    IOCSRRD.B IOCSRRD.H IOCSRRD.W IOCSRRD.D IOCSRWR.B IOCSRWR.H IOCSRWR.W IOCSRWR.D
+    CACOP TLBP(TLBSRCH) TLBRD TLBWR TLBFILL TLBCLR TLBFLUSH INVTLB LDDIR LDPTE
+
+Virtual Memory
+==============
+
+LoongArch supports direct-mapped virtual memory and page-mapped virtual memory.
+
+Direct-mapped virtual memory is configured by CSR.DMWn (n=0~3), it has a simple
+relationship between virtual address (VA) and physical address (PA)::
+
+ VA = PA + FixedOffset
+
+Page-mapped virtual memory has arbitrary relationship between VA and PA, which
+is recorded in TLB and page tables. LoongArch's TLB includes a fully-associative
+MTLB (Multiple Page Size TLB) and set-associative STLB (Single Page Size TLB).
+
+By default, the whole virtual address space of LA32 is configured like this:
+
+============ =========================== =============================
+Name         Address Range               Attributes
+============ =========================== =============================
+``UVRANGE``  ``0x00000000 - 0x7FFFFFFF`` Page-mapped, Cached, PLV0~3
+``KPRANGE0`` ``0x80000000 - 0x9FFFFFFF`` Direct-mapped, Uncached, PLV0
+``KPRANGE1`` ``0xA0000000 - 0xBFFFFFFF`` Direct-mapped, Cached, PLV0
+``KVRANGE``  ``0xC0000000 - 0xFFFFFFFF`` Page-mapped, Cached, PLV0
+============ =========================== =============================
+
+User mode (PLV3) can only access UVRANGE. For direct-mapped KPRANGE0 and
+KPRANGE1, PA is equal to VA with bit30~31 cleared. For example, the uncached
+direct-mapped VA of 0x00001000 is 0x80001000, and the cached direct-mapped
+VA of 0x00001000 is 0xA0001000.
+
+By default, the whole virtual address space of LA64 is configured like this:
+
+============ ====================== ======================================
+Name         Address Range          Attributes
+============ ====================== ======================================
+``XUVRANGE`` ``0x0000000000000000 - Page-mapped, Cached, PLV0~3
+             0x3FFFFFFFFFFFFFFF``
+``XSPRANGE`` ``0x4000000000000000 - Direct-mapped, Cached / Uncached, PLV0
+             0x7FFFFFFFFFFFFFFF``
+``XKPRANGE`` ``0x8000000000000000 - Direct-mapped, Cached / Uncached, PLV0
+             0xBFFFFFFFFFFFFFFF``
+``XKVRANGE`` ``0xC000000000000000 - Page-mapped, Cached, PLV0
+             0xFFFFFFFFFFFFFFFF``
+============ ====================== ======================================
+
+User mode (PLV3) can only access XUVRANGE. For direct-mapped XSPRANGE and
+XKPRANGE, PA is equal to VA with bits 60~63 cleared, and the cache attribute
+is configured by bits 60~61 in VA: 0 is for strongly-ordered uncached, 1 is
+for coherent cached, and 2 is for weakly-ordered uncached.
+
+Currently we only use XKPRANGE for direct mapping and XSPRANGE is reserved.
+
+To put this in action: the strongly-ordered uncached direct-mapped VA (in
+XKPRANGE) of 0x00000000_00001000 is 0x80000000_00001000, the coherent cached
+direct-mapped VA (in XKPRANGE) of 0x00000000_00001000 is 0x90000000_00001000,
+and the weakly-ordered uncached direct-mapped VA (in XKPRANGE) of 0x00000000
+_00001000 is 0xA0000000_00001000.
+
+Relationship of Loongson and LoongArch
+======================================
+
+LoongArch is a RISC ISA which is different from any other existing ones, while
+Loongson is a family of processors. Loongson includes 3 series: Loongson-1 is
+the 32-bit processor series, Loongson-2 is the low-end 64-bit processor series,
+and Loongson-3 is the high-end 64-bit processor series. Old Loongson is based on
+MIPS, while New Loongson is based on LoongArch. Take Loongson-3 as an example:
+Loongson-3A1000/3B1500/3A2000/3A3000/3A4000 are MIPS-compatible, while Loongson-
+3A5000 (and future revisions) are all based on LoongArch.
+
+.. _loongarch-references:
+
+References
+==========
+
+Official web site of Loongson Technology Corp. Ltd.:
+
+  http://www.loongson.cn/
+
+Developer web site of Loongson and LoongArch (Software and Documentation):
+
+  http://www.loongnix.cn/
+
+  https://github.com/loongson/
+
+  https://loongson.github.io/LoongArch-Documentation/
+
+Documentation of LoongArch ISA:
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-Vol1-v1.02-CN.pdf (in Chinese)
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-Vol1-v1.02-EN.pdf (in English)
+
+Documentation of LoongArch ELF psABI:
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-ELF-ABI-v2.00-CN.pdf (in Chinese)
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-ELF-ABI-v2.00-EN.pdf (in English)
+
+Linux kernel repository of Loongson and LoongArch:
+
+  https://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson.git
diff --git a/Documentation/arch/loongarch/irq-chip-model.rst b/Documentation/arch/loongarch/irq-chip-model.rst
new file mode 100644
index 000000000000..7988f4192363
--- /dev/null
+++ b/Documentation/arch/loongarch/irq-chip-model.rst
@@ -0,0 +1,160 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================================
+IRQ chip model (hierarchy) of LoongArch
+=======================================
+
+Currently, LoongArch based processors (e.g. Loongson-3A5000) can only work together
+with LS7A chipsets. The irq chips in LoongArch computers include CPUINTC (CPU Core
+Interrupt Controller), LIOINTC (Legacy I/O Interrupt Controller), EIOINTC (Extended
+I/O Interrupt Controller), HTVECINTC (Hyper-Transport Vector Interrupt Controller),
+PCH-PIC (Main Interrupt Controller in LS7A chipset), PCH-LPC (LPC Interrupt Controller
+in LS7A chipset) and PCH-MSI (MSI Interrupt Controller).
+
+CPUINTC is a per-core controller (in CPU), LIOINTC/EIOINTC/HTVECINTC are per-package
+controllers (in CPU), while PCH-PIC/PCH-LPC/PCH-MSI are controllers out of CPU (i.e.,
+in chipsets). These controllers (in other words, irqchips) are linked in a hierarchy,
+and there are two models of hierarchy (legacy model and extended model).
+
+Legacy IRQ model
+================
+
+In this model, IPI (Inter-Processor Interrupt) and CPU Local Timer interrupt go
+to CPUINTC directly, CPU UARTS interrupts go to LIOINTC, while all other devices
+interrupts go to PCH-PIC/PCH-LPC/PCH-MSI and gathered by HTVECINTC, and then go
+to LIOINTC, and then CPUINTC::
+
+     +-----+     +---------+     +-------+
+     | IPI | --> | CPUINTC | <-- | Timer |
+     +-----+     +---------+     +-------+
+                      ^
+                      |
+                 +---------+     +-------+
+                 | LIOINTC | <-- | UARTs |
+                 +---------+     +-------+
+                      ^
+                      |
+                +-----------+
+                | HTVECINTC |
+                +-----------+
+                 ^         ^
+                 |         |
+           +---------+ +---------+
+           | PCH-PIC | | PCH-MSI |
+           +---------+ +---------+
+             ^     ^           ^
+             |     |           |
+     +---------+ +---------+ +---------+
+     | PCH-LPC | | Devices | | Devices |
+     +---------+ +---------+ +---------+
+          ^
+          |
+     +---------+
+     | Devices |
+     +---------+
+
+Extended IRQ model
+==================
+
+In this model, IPI (Inter-Processor Interrupt) and CPU Local Timer interrupt go
+to CPUINTC directly, CPU UARTS interrupts go to LIOINTC, while all other devices
+interrupts go to PCH-PIC/PCH-LPC/PCH-MSI and gathered by EIOINTC, and then go to
+to CPUINTC directly::
+
+          +-----+     +---------+     +-------+
+          | IPI | --> | CPUINTC | <-- | Timer |
+          +-----+     +---------+     +-------+
+                       ^       ^
+                       |       |
+                +---------+ +---------+     +-------+
+                | EIOINTC | | LIOINTC | <-- | UARTs |
+                +---------+ +---------+     +-------+
+                 ^       ^
+                 |       |
+          +---------+ +---------+
+          | PCH-PIC | | PCH-MSI |
+          +---------+ +---------+
+            ^     ^           ^
+            |     |           |
+    +---------+ +---------+ +---------+
+    | PCH-LPC | | Devices | | Devices |
+    +---------+ +---------+ +---------+
+         ^
+         |
+    +---------+
+    | Devices |
+    +---------+
+
+ACPI-related definitions
+========================
+
+CPUINTC::
+
+  ACPI_MADT_TYPE_CORE_PIC;
+  struct acpi_madt_core_pic;
+  enum acpi_madt_core_pic_version;
+
+LIOINTC::
+
+  ACPI_MADT_TYPE_LIO_PIC;
+  struct acpi_madt_lio_pic;
+  enum acpi_madt_lio_pic_version;
+
+EIOINTC::
+
+  ACPI_MADT_TYPE_EIO_PIC;
+  struct acpi_madt_eio_pic;
+  enum acpi_madt_eio_pic_version;
+
+HTVECINTC::
+
+  ACPI_MADT_TYPE_HT_PIC;
+  struct acpi_madt_ht_pic;
+  enum acpi_madt_ht_pic_version;
+
+PCH-PIC::
+
+  ACPI_MADT_TYPE_BIO_PIC;
+  struct acpi_madt_bio_pic;
+  enum acpi_madt_bio_pic_version;
+
+PCH-MSI::
+
+  ACPI_MADT_TYPE_MSI_PIC;
+  struct acpi_madt_msi_pic;
+  enum acpi_madt_msi_pic_version;
+
+PCH-LPC::
+
+  ACPI_MADT_TYPE_LPC_PIC;
+  struct acpi_madt_lpc_pic;
+  enum acpi_madt_lpc_pic_version;
+
+References
+==========
+
+Documentation of Loongson-3A5000:
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-3A5000-usermanual-1.02-CN.pdf (in Chinese)
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-3A5000-usermanual-1.02-EN.pdf (in English)
+
+Documentation of Loongson's LS7A chipset:
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-7A1000-usermanual-2.00-CN.pdf (in Chinese)
+
+  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/Loongson-7A1000-usermanual-2.00-EN.pdf (in English)
+
+.. Note::
+    - CPUINTC is CSR.ECFG/CSR.ESTAT and its interrupt controller described
+      in Section 7.4 of "LoongArch Reference Manual, Vol 1";
+    - LIOINTC is "Legacy I/OInterrupts" described in Section 11.1 of
+      "Loongson 3A5000 Processor Reference Manual";
+    - EIOINTC is "Extended I/O Interrupts" described in Section 11.2 of
+      "Loongson 3A5000 Processor Reference Manual";
+    - HTVECINTC is "HyperTransport Interrupts" described in Section 14.3 of
+      "Loongson 3A5000 Processor Reference Manual";
+    - PCH-PIC/PCH-MSI is "Interrupt Controller" described in Section 5 of
+      "Loongson 7A1000 Bridge User Manual";
+    - PCH-LPC is "LPC Interrupts" described in Section 24.3 of
+      "Loongson 7A1000 Bridge User Manual".