Re: [PATCH V2 1/3] riscv: Add Zicbop instruction definitions & cpufeature

Leonardo Bras
2024-01-03T19:07:20Z

On Tue, Jan 02, 2024 at 11:32:44AM +0100, Andrew Jones wrote:
> On Sun, Dec 31, 2023 at 03:29:51AM -0500, guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > Cache-block prefetch instructions are HINTs to the hardware to
> > indicate that software intends to perform a particular type of
> > memory access in the near future. This patch adds prefetch.i,
> > prefetch.r and prefetch.w instruction definitions by
> > RISCV_ISA_EXT_ZICBOP cpufeature.
>
> It also adds S-type instruction encoding support which isn't mentioned.
> Actually, it'd probably be best to put the new instruction encoding in
> its own separate patch.
>
> >
> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > ---
> > arch/riscv/Kconfig | 15 ++++++++
> > arch/riscv/include/asm/hwcap.h | 1 +
> > arch/riscv/include/asm/insn-def.h | 60 +++++++++++++++++++++++++++++++
> > arch/riscv/kernel/cpufeature.c | 1 +
> > 4 files changed, 77 insertions(+)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 24c1799e2ec4..fcbd417d65ea 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -579,6 +579,21 @@ config RISCV_ISA_ZICBOZ
> >
> > If you don't know what to do here, say Y.
> >
> > +config RISCV_ISA_ZICBOP
> > + bool "Zicbop extension support for cache block prefetch"
> > + depends on MMU
> > + depends on RISCV_ALTERNATIVE
> > + default y
> > + help
> > + Adds support to dynamically detect the presence of the ZICBOP
> > + extension (Cache Block Prefetch Operations) and enable its
> > + usage.
> > +
> > + The Zicbop extension can be used to prefetch cache block for
>
> blocks
>
> > + read/write fetch.
> > +
> > + If you don't know what to do here, say Y.
> > +
> > config TOOLCHAIN_HAS_ZIHINTPAUSE
> > bool
> > default y
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index 06d30526ef3b..77d3b6ee25ab 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -57,6 +57,7 @@
> > #define RISCV_ISA_EXT_ZIHPM 42
> > #define RISCV_ISA_EXT_SMSTATEEN 43
> > #define RISCV_ISA_EXT_ZICOND 44
> > +#define RISCV_ISA_EXT_ZICBOP 45
> >
> > #define RISCV_ISA_EXT_MAX 64
> >
> > diff --git a/arch/riscv/include/asm/insn-def.h b/arch/riscv/include/asm/insn-def.h
> > index e27179b26086..bbda350a63bf 100644
> > --- a/arch/riscv/include/asm/insn-def.h
> > +++ b/arch/riscv/include/asm/insn-def.h
> > @@ -18,6 +18,13 @@
> > #define INSN_I_RD_SHIFT 7
> > #define INSN_I_OPCODE_SHIFT 0
> >
> > +#define INSN_S_SIMM7_SHIFT 25
> > +#define INSN_S_RS2_SHIFT 20
> > +#define INSN_S_RS1_SHIFT 15
> > +#define INSN_S_FUNC3_SHIFT 12
> > +#define INSN_S_SIMM5_SHIFT 7
> > +#define INSN_S_OPCODE_SHIFT 0
> > +
> > #ifdef __ASSEMBLY__
> >
> > #ifdef CONFIG_AS_HAS_INSN
> > @@ -30,6 +37,10 @@
> > .insn i \opcode, \func3, \rd, \rs1, \simm12
> > .endm
> >
> > + .macro insn_s, opcode, func3, rs2, simm12, rs1
> > + .insn s \opcode, \func3, \rs2, \simm12(\rs1)
> > + .endm
> > +
> > #else
> >
> > #include <asm/gpr-num.h>
> > @@ -51,10 +62,20 @@
> > (\simm12 << INSN_I_SIMM12_SHIFT))
> > .endm
> >
> > + .macro insn_s, opcode, func3, rs2, simm12, rs1
> > + .4byte ((\opcode << INSN_S_OPCODE_SHIFT) | \
> > + (\func3 << INSN_S_FUNC3_SHIFT) | \
> > + (.L__gpr_num_\rs2 << INSN_S_RS2_SHIFT) | \
> > + (.L__gpr_num_\rs1 << INSN_S_RS1_SHIFT) | \
> > + ((\simm12 & 0x1f) << INSN_S_SIMM5_SHIFT) | \
> > + (((\simm12 >> 5) & 0x7f) << INSN_S_SIMM7_SHIFT))
> > + .endm
> > +
> > #endif
> >
> > #define __INSN_R(...) insn_r __VA_ARGS__
> > #define __INSN_I(...) insn_i __VA_ARGS__
> > +#define __INSN_S(...) insn_s __VA_ARGS__
> >
> > #else /* ! __ASSEMBLY__ */
> >
> > @@ -66,6 +87,9 @@
> > #define __INSN_I(opcode, func3, rd, rs1, simm12) \
> > ".insn i " opcode ", " func3 ", " rd ", " rs1 ", " simm12 "\n"
> >
> > +#define __INSN_S(opcode, func3, rs2, simm12, rs1) \
> > + ".insn s " opcode ", " func3 ", " rs2 ", " simm12 "(" rs1 ")\n"
> > +
> > #else
> >
> > #include <linux/stringify.h>
> > @@ -92,12 +116,26 @@
> > " (\\simm12 << " __stringify(INSN_I_SIMM12_SHIFT) "))\n" \
> > " .endm\n"
> >
> > +#define DEFINE_INSN_S \
> > + __DEFINE_ASM_GPR_NUMS \
> > +" .macro insn_s, opcode, func3, rs2, simm12, rs1\n" \
> > +" .4byte ((\\opcode << " __stringify(INSN_S_OPCODE_SHIFT) ") |" \
> > +" (\\func3 << " __stringify(INSN_S_FUNC3_SHIFT) ") |" \
> > +" (.L__gpr_num_\\rs2 << " __stringify(INSN_S_RS2_SHIFT) ") |" \
> > +" (.L__gpr_num_\\rs1 << " __stringify(INSN_S_RS1_SHIFT) ") |" \
> > +" ((\\simm12 & 0x1f) << " __stringify(INSN_S_SIMM5_SHIFT) ") |" \
> > +" (((\\simm12 >> 5) & 0x7f) << " __stringify(INSN_S_SIMM7_SHIFT) "))\n" \
> > +" .endm\n"
> > +
> > #define UNDEFINE_INSN_R \
> > " .purgem insn_r\n"
> >
> > #define UNDEFINE_INSN_I \
> > " .purgem insn_i\n"
> >
> > +#define UNDEFINE_INSN_S \
> > +" .purgem insn_s\n"
> > +
> > #define __INSN_R(opcode, func3, func7, rd, rs1, rs2) \
> > DEFINE_INSN_R \
> > "insn_r " opcode ", " func3 ", " func7 ", " rd ", " rs1 ", " rs2 "\n" \
> > @@ -108,6 +146,11 @@
> > "insn_i " opcode ", " func3 ", " rd ", " rs1 ", " simm12 "\n" \
> > UNDEFINE_INSN_I
> >
> > +#define __INSN_S(opcode, func3, rs2, simm12, rs1) \
> > + DEFINE_INSN_S \
> > + "insn_s " opcode ", " func3 ", " rs2 ", " simm12 ", " rs1 "\n" \
> > + UNDEFINE_INSN_S
> > +
> > #endif
> >
> > #endif /* ! __ASSEMBLY__ */
> > @@ -120,6 +163,10 @@
> > __INSN_I(RV_##opcode, RV_##func3, RV_##rd, \
> > RV_##rs1, RV_##simm12)
> >
> > +#define INSN_S(opcode, func3, rs2, simm12, rs1) \
> > + __INSN_S(RV_##opcode, RV_##func3, RV_##rs2, \
> > + RV_##simm12, RV_##rs1)
> > +
> > #define RV_OPCODE(v) __ASM_STR(v)
> > #define RV_FUNC3(v) __ASM_STR(v)
> > #define RV_FUNC7(v) __ASM_STR(v)
> > @@ -133,6 +180,7 @@
> > #define RV___RS2(v) __RV_REG(v)
> >
> > #define RV_OPCODE_MISC_MEM RV_OPCODE(15)
> > +#define RV_OPCODE_OP_IMM RV_OPCODE(19)
> > #define RV_OPCODE_SYSTEM RV_OPCODE(115)
> >
> > #define HFENCE_VVMA(vaddr, asid) \
> > @@ -196,4 +244,16 @@
> > INSN_I(OPCODE_MISC_MEM, FUNC3(2), __RD(0), \
> > RS1(base), SIMM12(4))
> >
> > +#define CBO_PREFETCH_I(base, offset) \
> > + INSN_S(OPCODE_OP_IMM, FUNC3(6), __RS2(0), \
> > + SIMM12(offset), RS1(base))
> > +
> > +#define CBO_PREFETCH_R(base, offset) \
> > + INSN_S(OPCODE_OP_IMM, FUNC3(6), __RS2(1), \
> > + SIMM12(offset), RS1(base))
> > +
> > +#define CBO_PREFETCH_W(base, offset) \
> > + INSN_S(OPCODE_OP_IMM, FUNC3(6), __RS2(3), \
> > + SIMM12(offset), RS1(base))
>
> Shouldn't we ensure the lower 5-bits of offset are zero by masking it?

Note for my future self, read other reviews before doing my own :)

>
> > +
> > #endif /* __ASM_INSN_DEF_H */
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index b3785ffc1570..bdb02b066041 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -168,6 +168,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
> > __RISCV_ISA_EXT_DATA(h, RISCV_ISA_EXT_h),
> > __RISCV_ISA_EXT_DATA(zicbom, RISCV_ISA_EXT_ZICBOM),
> > __RISCV_ISA_EXT_DATA(zicboz, RISCV_ISA_EXT_ZICBOZ),
> > + __RISCV_ISA_EXT_DATA(zicbop, RISCV_ISA_EXT_ZICBOP),
>
> zicbop should be above zicboz (alphabetical)
>
> > __RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
> > __RISCV_ISA_EXT_DATA(zicond, RISCV_ISA_EXT_ZICOND),
> > __RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
> > --
> > 2.40.1
> >
>
> Thanks,
> drew