linux-kernel - Re: [PATCH v5 3/6] RISC-V: Extract multi-letter extension names from "riscv, isa"

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Date:   Mon, 28 Feb 2022 15:33:51 +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>,
        Tsukasa OI <research_trasio@....a4lg.com>,
        Heiko Stuebner <heiko@...ech.de>,
        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 v5 3/6] RISC-V: Extract multi-letter extension names from
 "riscv, isa"

On Wed, Feb 23, 2022 at 2:18 AM Atish Patra <atishp@...osinc.com> wrote:
>
> From: Tsukasa OI <research_trasio@....a4lg.com>
>
> Currently, there is no usage for version numbers in extensions as
> any ratified non base ISA extension will always at v1.0.
>
> Extract the extension names in place for future parsing.
>
> Tested-by: Heiko Stuebner <heiko@...ech.de>
> Reviewed-by: Anup Patel <anup@...infault.org>
> Signed-off-by: Tsukasa OI <research_trasio@....a4lg.com>
> [Improved commit text and comments]
> Signed-off-by: Atish Patra <atishp@...osinc.com>

Looks good to me.

Reviewed-by: Anup Patel <anup@...infault.org>

Regards,
Anup

> ---
>  arch/riscv/kernel/cpufeature.c | 35 ++++++++++++++++++++++++++--------
>  1 file changed, 27 insertions(+), 8 deletions(-)
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 72c5f6ef56b5..b0df7eff47f7 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -124,8 +124,28 @@ void __init riscv_fill_hwcap(void)
>                                 ext_long = true;
>                                 /* Multi-letter extension must be delimited */
>                                 for (; *isa && *isa != '_'; ++isa)
> -                                       if (!islower(*isa) && !isdigit(*isa))
> +                                       if (unlikely(!islower(*isa)
> +                                                    && !isdigit(*isa)))
>                                                 ext_err = true;
> +                               /* Parse backwards */
> +                               ext_end = isa;
> +                               if (unlikely(ext_err))
> +                                       break;
> +                               if (!isdigit(ext_end[-1]))
> +                                       break;
> +                               /* Skip the minor version */
> +                               while (isdigit(*--ext_end))
> +                                       ;
> +                               if (ext_end[0] != 'p'
> +                                   || !isdigit(ext_end[-1])) {
> +                                       /* Advance it to offset the pre-decrement */
> +                                       ++ext_end;
> +                                       break;
> +                               }
> +                               /* Skip the major version */
> +                               while (isdigit(*--ext_end))
> +                                       ;
> +                               ++ext_end;
>                                 break;
>                         default:
>                                 if (unlikely(!islower(*ext))) {
> @@ -151,14 +171,13 @@ void __init riscv_fill_hwcap(void)
>                         }
>                         if (*isa != '_')
>                                 --isa;
> -                       /*
> -                        * TODO: Full version-aware handling including
> -                        * multi-letter extensions will be added in-future.
> -                        */
> -                       if (ext_err || ext_long)
> +
> +                       if (unlikely(ext_err))
>                                 continue;
> -                       this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
> -                       this_isa |= (1UL << (*ext - 'a'));
> +                       if (!ext_long) {
> +                               this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
> +                               this_isa |= (1UL << (*ext - 'a'));
> +                       }
>                 }
>
>                 /*
> --
> 2.30.2
>