--- /dev/null
+.. 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/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-v1.00-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 psABI:
+
+ 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
--- /dev/null
+.. 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".
projects / kernel.git / commitdiff