Re: [PATCH v2 06/10] riscv: Implement xchg8/16() using Zabha

Alexandre Ghiti
2024-07-15T13:20:44Z

Hi Guo,

On Wed, Jul 10, 2024 at 3:37 AM Guo Ren <guoren@kernel.org> wrote:
>
> On Wed, Jun 26, 2024 at 9:10 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
> >
> > This adds runtime support for Zabha in xchg8/16() operations.
> >
> > Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> > ---
> > arch/riscv/include/asm/cmpxchg.h | 33 +++++++++++++++++++++++++++++---
> > arch/riscv/include/asm/hwcap.h | 1 +
> > arch/riscv/kernel/cpufeature.c | 1 +
> > 3 files changed, 32 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> > index da42f32ea53d..eb35e2d30a97 100644
> > --- a/arch/riscv/include/asm/cmpxchg.h
> > +++ b/arch/riscv/include/asm/cmpxchg.h
> > @@ -11,8 +11,17 @@
> > #include <asm/fence.h>
> > #include <asm/alternative.h>
> >
> > -#define __arch_xchg_masked(sc_sfx, prepend, append, r, p, n) \
> > +#define __arch_xchg_masked(sc_sfx, swap_sfx, prepend, sc_append, \
> > + swap_append, r, p, n) \
> > ({ \
> > + __label__ zabha, end; \
> > + \
> > + if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
> > + asm goto(ALTERNATIVE("nop", "j %[zabha]", 0, \
> > + RISCV_ISA_EXT_ZABHA, 1) \
> > + : : : : zabha); \
> > + } \
> > + \
> Could we exchange the sequence between Zabha & lr/sc?
> I mean:
> nop -> zabha
> j -> lr/sc
>

Yes, you're right, it makes more sense this way. I'll do that.

Thanks,

Alex

>
> > u32 *__ptr32b = (u32 *)((ulong)(p) & ~0x3); \
> > ulong __s = ((ulong)(p) & (0x4 - sizeof(*p))) * BITS_PER_BYTE; \
> > ulong __mask = GENMASK(((sizeof(*p)) * BITS_PER_BYTE) - 1, 0) \
> > @@ -28,12 +37,25 @@
> > " or %1, %1, %z3\n" \
> > " sc.w" sc_sfx " %1, %1, %2\n" \
> > " bnez %1, 0b\n" \
> > - append \
> > + sc_append \
> > : "=&r" (__retx), "=&r" (__rc), "+A" (*(__ptr32b)) \
> > : "rJ" (__newx), "rJ" (~__mask) \
> > : "memory"); \
> > \
> > r = (__typeof__(*(p)))((__retx & __mask) >> __s); \
> > + goto end; \
> > + \
> > +zabha:
> jump lr/sc implementation because it's already slow.
> \
> > + if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
> > + __asm__ __volatile__ ( \
> > + prepend \
> > + " amoswap" swap_sfx " %0, %z2, %1\n" \
> > + swap_append \
> > + : "=&r" (r), "+A" (*(p)) \
> > + : "rJ" (n) \
> > + : "memory"); \
> > + } \
> > +end:; \
> > })
> >
> > #define __arch_xchg(sfx, prepend, append, r, p, n) \
> > @@ -56,8 +78,13 @@
> > \
> > switch (sizeof(*__ptr)) { \
> > case 1: \
> > + __arch_xchg_masked(sc_sfx, ".b" swap_sfx, \
> > + prepend, sc_append, swap_append, \
> > + __ret, __ptr, __new); \
> > + break; \
> > case 2: \
> > - __arch_xchg_masked(sc_sfx, prepend, sc_append, \
> > + __arch_xchg_masked(sc_sfx, ".h" swap_sfx, \
> > + prepend, sc_append, swap_append, \
> > __ret, __ptr, __new); \
> > break; \
> > case 4: \
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index e17d0078a651..f71ddd2ca163 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -81,6 +81,7 @@
> > #define RISCV_ISA_EXT_ZTSO 72
> > #define RISCV_ISA_EXT_ZACAS 73
> > #define RISCV_ISA_EXT_XANDESPMU 74
> > +#define RISCV_ISA_EXT_ZABHA 75
> >
> > #define RISCV_ISA_EXT_XLINUXENVCFG 127
> >
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 5ef48cb20ee1..c125d82c894b 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -257,6 +257,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
> > __RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
> > __RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
> > __RISCV_ISA_EXT_DATA(zacas, RISCV_ISA_EXT_ZACAS),
> > + __RISCV_ISA_EXT_DATA(zabha, RISCV_ISA_EXT_ZABHA),
> > __RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
> > __RISCV_ISA_EXT_DATA(zfh, RISCV_ISA_EXT_ZFH),
> > __RISCV_ISA_EXT_DATA(zfhmin, RISCV_ISA_EXT_ZFHMIN),
> > --
> > 2.39.2
> >
>
>
> --
> Best Regards
> Guo Ren