Re: [PATCH v2 4/6] RISC-V: Implement multi-letter ISA extension probing framework

Heiko Stübner
2022-02-14T20:06:18Z

Am Donnerstag, 10. Februar 2022, 22:40:16 CET schrieb Atish Patra:
> Multi-letter extensions can be probed using exising
> riscv_isa_extension_available API now. It doesn't support versioning
> right now as there is no use case for it.
> Individual extension specific implementation will be added during
> each extension support.
>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>

Tested-by: Heiko Stuebner <heiko@sntech.de>

By the way, does a similar parsing exist for opensbi as well?
Things like svpbmt as well as zicbom have CSR bits controlling how
these functions should behave (enabling them, etc), so I guess
opensbi also needs to parse the extensions from the ISA string?

Heiko

> ---
> arch/riscv/include/asm/hwcap.h | 18 ++++++++++++++++++
> arch/riscv/kernel/cpufeature.c | 27 ++++++++++++++++++++++++---
> 2 files changed, 42 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 5ce50468aff1..170bd80da520 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -34,7 +34,25 @@ extern unsigned long elf_hwcap;
> #define RISCV_ISA_EXT_s ('s' - 'a')
> #define RISCV_ISA_EXT_u ('u' - 'a')
>
> +/*
> + * Increse this to higher value as kernel support more ISA extensions.
> + */
> #define RISCV_ISA_EXT_MAX 64
> +#define RISCV_ISA_EXT_NAME_LEN_MAX 32
> +
> +/* The base ID for multi-letter ISA extensions */
> +#define RISCV_ISA_EXT_BASE 26
> +
> +/*
> + * This enum represent the logical ID for each multi-letter RISC-V ISA extension.
> + * The logical ID should start from RISCV_ISA_EXT_BASE and must not exceed
> + * RISCV_ISA_EXT_MAX. 0-25 range is reserved for single letter
> + * extensions while all the multi-letter extensions should define the next
> + * available logical extension id.
> + */
> +enum riscv_isa_ext_id {
> + RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
> +};
>
> unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index e9e3b0693d16..469b9739faf7 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -83,7 +83,7 @@ void __init riscv_fill_hwcap(void)
>
> for_each_of_cpu_node(node) {
> unsigned long this_hwcap = 0;
> - unsigned long this_isa = 0;
> + uint64_t this_isa = 0;
>
> if (riscv_of_processor_hartid(node) < 0)
> continue;
> @@ -169,12 +169,22 @@ void __init riscv_fill_hwcap(void)
> if (*isa != '_')
> --isa;
>
> +#define SET_ISA_EXT_MAP(name, bit) \
> + do { \
> + if ((ext_end - ext == sizeof(name) - 1) && \
> + !memcmp(ext, name, sizeof(name) - 1)) { \
> + this_isa |= (1UL << bit); \
> + pr_info("Found ISA extension %s", name);\
> + } \
> + } while (false) \
> +
> if (unlikely(ext_err))
> continue;
> if (!ext_long) {
> this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
> this_isa |= (1UL << (*ext - 'a'));
> }
> +#undef SET_ISA_EXT_MAP
> }
>
> /*
> @@ -187,10 +197,21 @@ void __init riscv_fill_hwcap(void)
> else
> elf_hwcap = this_hwcap;
>
> - if (riscv_isa[0])
> + if (riscv_isa[0]) {
> +#if IS_ENABLED(CONFIG_32BIT)
> + riscv_isa[0] &= this_isa & 0xFFFFFFFF;
> + riscv_isa[1] &= this_isa >> 32;
> +#else
> riscv_isa[0] &= this_isa;
> - else
> +#endif
> + } else {
> +#if IS_ENABLED(CONFIG_32BIT)
> + riscv_isa[0] = this_isa & 0xFFFFFFFF;
> + riscv_isa[1] = this_isa >> 32;
> +#else
> riscv_isa[0] = this_isa;
> +#endif
> + }
> }
>
> /* We don't support systems with F but without D, so mask those out