Re: [PATCH v2 03/10] riscv: Implement cmpxchg8/16() using Zabha

Andrea Parri
2024-06-29T19:20:32Z

> I admit that I found this all quite difficult to read; IIUC, this is
> missing an IS_ENABLED(CONFIG_RISCV_ISA_ZACAS) check. How about adding
> such a check under the zabha: label (replacing/in place of the second
> IS_ENABLED(CONFIG_RISCV_ISA_ZABHA) check) and moving the corresponding
> asm goto statement there, perhaps as follows? (on top of this patch)

[...]

> diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> index b9a3fdcec919..3c913afec150 100644
> --- a/arch/riscv/include/asm/cmpxchg.h
> +++ b/arch/riscv/include/asm/cmpxchg.h
> @@ -110,15 +110,12 @@
> __label__ no_zacas, zabha, end; \
> \
> if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
> - asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, \
> - RISCV_ISA_EXT_ZACAS, 1) \
> - : : : : no_zacas); \
> asm goto(ALTERNATIVE("nop", "j %[zabha]", 0, \
> RISCV_ISA_EXT_ZABHA, 1) \
> : : : : zabha); \
> } \
> \
> -no_zacas:; \
> +no_zacas: \
> 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) \
> @@ -148,16 +145,20 @@ no_zacas:; \
> goto end; \
> \
> zabha: \
> - if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
> - __asm__ __volatile__ ( \
> - prepend \
> - " amocas" cas_sfx " %0, %z2, %1\n" \
> - append \
> - : "+&r" (r), "+A" (*(p)) \
> - : "rJ" (n) \
> - : "memory"); \
> + if (IS_ENABLED(CONFIG_RISCV_ISA_ZAZAS)) { \
> + asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, \
> + RISCV_ISA_EXT_ZACAS, 1) \
> + : : : : no_zacas); \
> } \
> -end:; \
> + \
> + __asm__ __volatile__ ( \
> + prepend \
> + " amocas" cas_sfx " %0, %z2, %1\n" \
> + append \
> + : "+&r" (r), "+A" (*(p)) \
> + : "rJ" (n) \
> + : "memory"); \
> +end: \
> })
>
> #define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n) \

Unfortunately, this diff won't work e.g. when ZABHA is supported and
detected at boot while ZACAS is not supported; more thinking required...

Andrea