linux-kernel - Re: [PATCH v3 4/6] RISC-V: Implement multi-letter ISA extension probing framework

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Message-ID: <CAAhSdy29nzXFesfeMjY_FkTmTZ4yrHjGxTweBCVn-wFFHnMV=A@mail.gmail.com>
Date:   Tue, 15 Feb 2022 15:53:54 +0530
From:   Anup Patel <anup@...infault.org>
To:     Atish Patra <atishp@...osinc.com>
Cc:     "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atishp@...shpatra.org>,
        Damien Le Moal <damien.lemoal@....com>,
        DTML <devicetree@...r.kernel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v3 4/6] RISC-V: Implement multi-letter ISA extension
 probing framework

On Tue, Feb 15, 2022 at 2:32 PM Atish Patra <atishp@...osinc.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.
>
> Signed-off-by: Atish Patra <atishp@...osinc.com>
> ---
>  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 cd9eb34f8d11..af9a57ad3d4e 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;

Why not use a bitmap here ?

>
>                 if (riscv_of_processor_hartid(node) < 0)
>                         continue;
> @@ -167,12 +167,22 @@ void __init riscv_fill_hwcap(void)
>                         if (*isa != '_')
>                                 --isa;
>
> +#define SET_ISA_EXT_MAP(name, bit)                                             \

Where is this macro used ?

> +                       do {                                                    \
> +                               if ((ext_end - ext == sizeof(name) - 1) &&      \
> +                                    !memcmp(ext, name, sizeof(name) - 1)) {    \
> +                                       this_isa |= (1UL << bit);               \

You can use set_bit() here when using bitmap.

> +                                       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
>                 }
>
>                 /*
> @@ -185,10 +195,21 @@ void __init riscv_fill_hwcap(void)
>                 else
>                         elf_hwcap = this_hwcap;
>
> -               if (riscv_isa[0])
> +               if (riscv_isa[0]) {

You can use bitmap_weight() here

> +#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
> --
> 2.30.2
>

Regards,
Anup