linux-kernel - Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR

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Date:   Wed, 22 Mar 2023 09:04:25 -0700
From:   Evan Green <evan@...osinc.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Palmer Dabbelt <palmer@...osinc.com>, slewis@...osinc.com,
        heiko@...ech.de, vineetg@...osinc.com,
        Conor Dooley <conor.dooley@...rochip.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Bresticker <abrestic@...osinc.com>,
        Celeste Liu <coelacanthus@...look.com>,
        Guo Ren <guoren@...nel.org>, Jonathan Corbet <corbet@....net>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 3/6] RISC-V: hwprobe: Add support for RISCV_HWPROBE_BASE_BEHAVIOR_IMA

Yep, you and Heiko are on the same wavelength these days. I'll make that change.
-Evan

On Wed, Mar 22, 2023 at 8:36 AM Conor Dooley <conor@...nel.org> wrote:
>
> On Tue, Mar 14, 2023 at 11:32:17AM -0700, Evan Green wrote:
> > We have an implicit set of base behaviors that userspace depends on,
> > which are mostly defined in various ISA specifications.
> >
> > Co-developed-by: Palmer Dabbelt <palmer@...osinc.com>
> > Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
> > Signed-off-by: Evan Green <evan@...osinc.com>
> > Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
>
> > @@ -125,6 +126,25 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
> >       case RISCV_HWPROBE_KEY_MIMPID:
> >               hwprobe_arch_id(pair, cpus);
> >               break;
> > +     /*
> > +      * The kernel already assumes that the base single-letter ISA
> > +      * extensions are supported on all harts, and only supports the
> > +      * IMA base, so just cheat a bit here and tell that to
> > +      * userspace.
> > +      */
> > +     case RISCV_HWPROBE_KEY_BASE_BEHAVIOR:
> > +             pair->value = RISCV_HWPROBE_BASE_BEHAVIOR_IMA;
> > +             break;
> > +
> > +     case RISCV_HWPROBE_KEY_IMA_EXT_0:
> > +             pair->value = 0;
> > +             if (has_fpu())
> > +                     pair->value |= RISCV_HWPROBE_IMA_FD;
> > +
> > +             if (elf_hwcap & RISCV_ISA_EXT_c)
>
> Random thought while reviewing another patch, and I kinda felt a bit
> stupid following the existing code to try and make sure, but should this
> become a call to riscv_isa_extension_available(NULL, c)?
> It may be nice to propagate that helper, if it works, than check the bit
> directly.
>
> Cheers,
> Conor.
>
> > +                     pair->value |= RISCV_HWPROBE_IMA_C;
> > +
> > +             break;
> >
> >       /*
> >        * For forward compatibility, unknown keys don't fail the whole
> > --
> > 2.25.1
> >