[PATCH v5 4/6] RISC-V: Implement multi-letter ISA extension probing framework

[Anup Patel]

On Wed, Feb 23, 2022 at 2:18 AM Atish Patra <atishp at rivosinc.com> wrote:
>
> 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.
>
> Tested-by: Heiko Stuebner <heiko at sntech.de>
> Signed-off-by: Atish Patra <atishp at rivosinc.com>

Looks good to me.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup

> ---
>  arch/riscv/include/asm/hwcap.h | 18 ++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c | 24 ++++++++++++++++++------
>  2 files changed, 36 insertions(+), 6 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 b0df7eff47f7..c6693873e95c 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;
> +               DECLARE_BITMAP(this_isa, RISCV_ISA_EXT_MAX);
>
>                 if (riscv_of_processor_hartid(node) < 0)
>                         continue;
> @@ -100,6 +100,7 @@ void __init riscv_fill_hwcap(void)
>                 if (!strncmp(isa, "rv64", 4))
>                         isa += 4;
>  #endif
> +               bitmap_zero(this_isa, RISCV_ISA_EXT_MAX);
>                 for (; *isa; ++isa) {
>                         const char *ext = isa++;
>                         const char *ext_end = isa;
> @@ -172,12 +173,22 @@ 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)) {    \
> +                                       set_bit(bit, this_isa);                 \
> +                                       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'));
> +                               set_bit(*ext - 'a', this_isa);
>                         }
> +#undef SET_ISA_EXT_MAP
>                 }
>
>                 /*
> @@ -190,10 +201,11 @@ void __init riscv_fill_hwcap(void)
>                 else
>                         elf_hwcap = this_hwcap;
>
> -               if (riscv_isa[0])
> -                       riscv_isa[0] &= this_isa;
> +               if (bitmap_weight(riscv_isa, RISCV_ISA_EXT_MAX))
> +                       bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
>                 else
> -                       riscv_isa[0] = this_isa;
> +                       bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
> +
>         }
>
>         /* We don't support systems with F but without D, so mask those out
> @@ -207,7 +219,7 @@ void __init riscv_fill_hwcap(void)
>         for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
>                 if (riscv_isa[0] & BIT_MASK(i))
>                         print_str[j++] = (char)('a' + i);
> -       pr_info("riscv: ISA extensions %s\n", print_str);
> +       pr_info("riscv: base ISA extensions %s\n", print_str);
>
>         memset(print_str, 0, sizeof(print_str));
>         for (i = 0, j = 0; i < NUM_ALPHA_EXTS; i++)
> --
> 2.30.2
>