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Date:   Sat, 14 May 2022 23:40:57 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     WANG Xuerui <kernel@...0n.name>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH V10 01/22] Documentation: LoongArch: Add basic documentations

Hi, Xuerui,

On Sat, May 14, 2022 at 9:11 PM WANG Xuerui <kernel@...0n.name> wrote:
>
> Hi,
>
> Overall it seems many of the review comments on v9 are not being
> respected, and there was no explanation or justification either. It's
> probably good netiquette (or rather, common sense) to give proper
> replies if you don't feel like changing some of the places.
>
> I've already privately contacted you about the overall disregard of my
> review comments, but for now I'll try to mentally diff the versions and
> review the fresher bits.
>
> On 5/14/22 16:03, Huacai Chen wrote:
> > Add some basic documentation for LoongArch. LoongArch is a new RISC ISA,
> > which is a bit like MIPS or RISC-V. LoongArch includes a reduced 32-bit
> > version (LA32R), a standard 32-bit version (LA32S) and a 64-bit version
> > (LA64).
> >
> > Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> > ---
> >   Documentation/arch.rst                     |   1 +
> >   Documentation/loongarch/features.rst       |   3 +
> >   Documentation/loongarch/index.rst          |  21 ++
> >   Documentation/loongarch/introduction.rst   | 353 +++++++++++++++++++++
> >   Documentation/loongarch/irq-chip-model.rst | 168 ++++++++++
> >   5 files changed, 546 insertions(+)
> >   create mode 100644 Documentation/loongarch/features.rst
> >   create mode 100644 Documentation/loongarch/index.rst
> >   create mode 100644 Documentation/loongarch/introduction.rst
> >   create mode 100644 Documentation/loongarch/irq-chip-model.rst
> >
> > diff --git a/Documentation/arch.rst b/Documentation/arch.rst
> > index 14bcd8294b93..41a66a8b38e4 100644
> > --- a/Documentation/arch.rst
> > +++ b/Documentation/arch.rst
> > @@ -13,6 +13,7 @@ implementation.
> >      arm/index
> >      arm64/index
> >      ia64/index
> > +   loongarch/index
> >      m68k/index
> >      mips/index
> >      nios2/index
> > diff --git a/Documentation/loongarch/features.rst b/Documentation/loongarch/features.rst
> > new file mode 100644
> > index 000000000000..ebacade3ea45
> > --- /dev/null
> > +++ b/Documentation/loongarch/features.rst
> > @@ -0,0 +1,3 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +.. kernel-feat:: $srctree/Documentation/features loongarch
> > diff --git a/Documentation/loongarch/index.rst b/Documentation/loongarch/index.rst
> > new file mode 100644
> > index 000000000000..d127e07a7ed3
> > --- /dev/null
> > +++ b/Documentation/loongarch/index.rst
> > @@ -0,0 +1,21 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +================================
> > +LoongArch-specific Documentation
> > +================================
> > +
> > +.. toctree::
> > +   :maxdepth: 2
> > +   :numbered:
> > +
> > +   introduction
> > +   irq-chip-model
> > +
> > +   features
> > +
> > +.. only::  subproject and html
> > +
> > +   Indices
> > +   =======
> > +
> > +   * :ref:`genindex`
> > diff --git a/Documentation/loongarch/introduction.rst b/Documentation/loongarch/introduction.rst
> > new file mode 100644
> > index 000000000000..7c7e512cfbcb
> > --- /dev/null
> > +++ b/Documentation/loongarch/introduction.rst
> > @@ -0,0 +1,353 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +=========================
> > +Introduction of LoongArch
> > +=========================
> > +
> > +LoongArch is a new RISC ISA, which is a bit like MIPS or RISC-V. LoongArch
> > +includes a reduced 32-bit version (LA32R), a standard 32-bit version (LA32S)
> > +and a 64-bit version (LA64). There are 4 privilege levels (PLVs) defined in
> > +LoongArch: PLV0~PLV3, from high to low. Kernel runs at PLV0 while applications
> > +run at PLV3. This document introduces the registers, basic instruction set,
> > +virtual memory and some other topics of LoongArch.
> > +
> > +Registers
> > +=========
> > +
> > +LoongArch registers include general purpose registers (GPRs), floating point
> > +registers (FPRs), vector registers (VRs) and control status registers (CSRs)
> > +used in privileged mode (PLV0).
> > +
> > +GPRs
> > +----
> > +
> > +LoongArch has 32 GPRs ($r0 - $r31), each one is 32bit wide in LA32 and 64bit
> > +wide in LA64. $r0 is always zero, and other registers has no special feature,
> > +but we actually have an ABI register convention as below.
> > +
> > +================= =============== =================== ============
> > +Name              Alias           Usage               Preserved
> > +                                                      across calls
> > +================= =============== =================== ============
> > +``$r0``           ``$zero``       Constant zero       Unused
> > +``$r1``           ``$ra``         Return address      No
> > +``$r2``           ``$tp``         TLS                 Unused
> > +``$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``          ``$u0``         Reserved            Unused
> > +``$r22``          ``$fp``         Frame pointer       Yes
> > +``$r23``-``$r31`` ``$s0``-``$s8`` Static registers    Yes
> > +================= =============== =================== ============
> > +
> > +Note: v0/v1 naming is deprecated, use a0/a1 instead. r21 is named u0
> > +in Linux kernel to save the percpu variables base address.
>
> Since the v0/v1 names are deprecated, we'd probably want to remove all
> mentions of them?
I want to keep this. At least when someone read old code, he/she can
know what it is.

>
> And the r21 has no ABI name, so you probably want to clarify a bit.
> Either change the "Reserved" to something like "(Kernel-specific) percpu
> base address", or remove the "$u0" from the table and replace with "n/a".
OK, replace with "n/a".

>
> > +
> > +FPRs
> > +----
> > +
> > +LoongArch has 32 FPRs ($f0 - $f31), each one is 64bit wide. We also have an
> The comment re "64bit wide" is not addressed since v9.
Both LA32 and LA64 have 64bit FPRs.

> > +ABI register conversion as below.
> > +
> > +================= ================== =================== ============
> > +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: fv0/fv1 naming is deprecated, use fa0/fa1 instead.
> Same for fv0/fv1.
> > +
> > +VRs
> > +----
> > +
> > +LoongArch has 128bit vector extension (LSX, short for Loongson SIMD eXtention)
> > +and 256bit vector extension (LASX, short for Loongson Advanced SIMD eXtension).
> > +There are also 32 vector registers, $v0 - $v31 for LSX and $x0 - $x31 for LASX.
> > +FPRs and VRs are overlapped, e.g. the lower 128bits of $x0 is $v0, and the lower
> > +64bits of $v0 is $f0, etc.
> While the word "overlap" is used, it feels wrong, just "FPRs and VRs
> overlap" would sound more natural.
OK, thanks.

> > +
> > +CSRs
> > +----
> > +
> > +CSRs can only be used in privileged mode (PLV0):
> > +
> > +================= ===================================== ==============
> > +Address           Full Name                             Abbrev Name
> > +================= ===================================== ==============
> > +0x0               Current Mode information              CRMD
> > +0x1               Pre-exception Mode information        PRMD
> > +0x2               Extended Unit Enable                  EUEN
> > +0x3               Miscellaneous control                 MISC
> > +0x4               Exception Configuration               ECFG
> > +0x5               Exception Status                      ESTAT
> > +0x6               Exception Return Address              ERA
> > +0x7               Bad Virtual Address                   BADV
> > +0x8               Bad Instruction                       BADI
> > +0xC               Exception Entry Base 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)   Data Save register                    SAVEn
> Hmm, now I have a better name -- "Saved Data register". Does that sound
> better than "Data Save"?
OK, thanks.

> > +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 Entry Base       TLBRENTRY
> > +                  address
> > +0x89              TLB Refill Exception BAD Virtual      TLBRBADV
> > +                  address
> > +0x8A              TLB Refill Exception Return Address   TLBRERA
> > +0x8B              TLB Refill Exception data SAVE        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 Entry Base    MERRENTRY
> > +                  address
> > +0x94              Machine Error Exception Return        MERRERA
> > +                  address
> > +0x95              Machine Error Exception data SAVE     MERRSAVE
> > +                  register
> The inconsistent capitalization is not fixed since v9.
OK, thanks.

> > +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             Fetch WatchPoint overall Control      FWPC
> > +0x381             Fetch WatchPoint overall Status       FWPS
> > +0x390+8n (0≤n≤7)  Fetch WatchPoint n Configuration 1    FWPnCFG1
> > +0x391+8n (0≤n≤7)  Fetch WatchPoint n Configuration 2    FWPnCFG2
> > +0x392+8n (0≤n≤7)  Fetch WatchPoint n Configuration 3    FWPnCFG3
> > +0x393+8n (0≤n≤7)  Fetch WatchPoint n Configuration 4    FWPnCFG4
> > +0x500             Debug register                        DBG
> > +0x501             Debug Exception Return address        DERA
> > +0x502             Debug data SAVE register              DSAVE
> > +================= ===================================== ==============
> > +
> > +ERA,TLBRERA,MERREEA and ERA sometimes are also called EPC,TLBREPC
> > +MERREPC and DEPC.
> > +
> > +Basic Instruction Set
> > +=====================
> > +
> > +Instruction formats
> > +-------------------
> > +
> > +LoongArch has 32-bit wide instructions, and there are 9 instruction formats::
>
> I forgot to mention this while reviewing v9, but obviously we have more
> formats (there are actually 39 in total [1]), so let's adjust this to
> say "9 basic instruction formats" instead. You really can't pretend
> there are only 9 formats when even ubiquitous ones like LU12I.W have
> formats not similar to any of the 9 listed.
OK, add a "basic".

>
> [1]: https://github.com/loongson-community/loongarch-opcodes
>
> > +
> > +  2R-type:    Opcode + Rj + Rd
> > +  3R-type:    Opcode + Rk + Rj + Rd
> > +  4R-type:    Opcode + Ra + Rk + Rj + Rd
> > +  2RI8-type:  Opcode + I8 + Rj + Rd
> > +  2RI12-type: Opcode + I12 + Rj + Rd
> > +  2RI14-type: Opcode + I14 + Rj + Rd
> > +  2RI16-type: Opcode + I16 + Rj + Rd
> > +  1RI21-type: Opcode + I21L + Rj + I21H
> > +  I26-type:   Opcode + I26L + I26H
> > +
> > +Rj and Rk are source operands (register), Rd is destination operand (register),
> > +and Ra is the additional operand (register) in 4R-type. I8/I12/I16/I21/I26 are
> Better reorder so Rd comes first, so that we describe from LSB to MSB.
> > +8-bits/12-bits/16-bits/21-bits/26bits immediate data. 21bits/26bits immediate
> > +data are split into higher bits and lower bits in an instruction word, so you
> > +can see I21L/I21H and I26L/I26H here.
Begin with opcode seems more natural.

> > +
> > +Instruction names (Mnemonics)
> > +-----------------------------
> > +
> > +We only list the instruction names here, for details please read the
> > +:ref:`references <loongarch-references>`.
> > +
> > +1. Arithmetic Operation 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
> Do we really have ADDU16I.D in the v1.00 manual? I'd want that in my
> binutils today! ;-)
> > +
> > +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 DBCL 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
>
> Why mention TLBP along with TLBSRCH? Is that an old name? If so you
> could revive names like DBGCALL, ERET and CACHE as well...
OK, add as well.

>
> Otherwise just remove it.
>
> > +
> > +Virtual Memory
> > +==============
> > +
> > +LoongArch can use 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
> So these names are not changed, despite I asked in v9 pointing out
> they're "awfully MIPS-like". And there is not the explanation for the
> name inventions either.
Just a name, we don't want to modify.

> > +============ =========================== =============================
> > +
> > +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 bit60~63 cleared, and the cache attributes is configured by
> > +bit60~61 (0 is strongly-ordered uncached, 1 is coherent cached, and 2 is weakly-
> > +ordered uncached) in VA. Currently we only use XKPRANGE for direct mapping and
> > +XSPRANGE is reserved. As an example, 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.
> This section is not reworked either.
Because it needn't rework.

> > +
> > +.. _loongarch-references:
> > +
> > +References
> > +==========
> > +
> > +Official web site of Loongson and LoongArch (Loongson Technology Corp. Ltd.):
> > +
> > +  http://www.loongson.cn/index.html
> > +
> > +Developer web site of Loongson and LoongArch (Software and Documentation):
> > +
> > +  http://www.loongnix.cn/index.php
> And the v9 suggestion here (better replace with link to the
> documentation repo than this user-facing portal).
The description here is "Software and Documentation", not just Documentation.

Huacai
> > +
> > +  https://github.com/loongson
> > +
> > +Documentation of LoongArch ISA:
> > +
> > +  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-Vol1-v1.00-CN.pdf (in Chinese)
> > +
> > +  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-Vol1-v1.00-EN.pdf (in English)
> > +
> > +Documentation of LoongArch ELF ABI:
> > +
> > +  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-ELF-ABI-v1.00-CN.pdf (in Chinese)
> > +
> > +  https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-ELF-ABI-v1.00-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/loongarch/irq-chip-model.rst b/Documentation/loongarch/irq-chip-model.rst
> > new file mode 100644
> > index 000000000000..35c962991283
> > --- /dev/null
> > +++ b/Documentation/loongarch/irq-chip-model.rst
> > @@ -0,0 +1,168 @@
> > +.. 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/O
> > +Interrupts" 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".

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