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diff --git a/Documentation/arch/loongarch/introduction.rst b/Documentation/arch/loongarch/introduction.rst new file mode 100644 index 0000000000..8c568cfc21 --- /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-v2.01-CN.pdf (in Chinese) + + https://github.com/loongson/LoongArch-Documentation/releases/latest/download/LoongArch-ELF-ABI-v2.01-EN.pdf (in English) + +Linux kernel repository of Loongson and LoongArch: + + https://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson.git |