linux-kernel - Re: [PATCH 14/19] riscv: hwprobe: Disambiguate vector and xtheadvector in hwprobe

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Message-ID: <CALs-HsviR8E-sRvzz7pd5eVGb4+XsAdG1hhbZOPf+m3Cu4JP_Q@mail.gmail.com>
Date: Fri, 12 Apr 2024 10:04:42 -0700
From: Evan Green <evan@...osinc.com>
To: Conor Dooley <conor.dooley@...rochip.com>
Cc: Charlie Jenkins <charlie@...osinc.com>, Conor Dooley <conor@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	Clément Léger <cleger@...osinc.com>, 
	Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>, linux-riscv@...ts.infradead.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Palmer Dabbelt <palmer@...osinc.com>, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, linux-doc@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 14/19] riscv: hwprobe: Disambiguate vector and
 xtheadvector in hwprobe

On Fri, Apr 12, 2024 at 4:35 AM Conor Dooley <conor.dooley@...rochip.com> wrote:
>
> On Thu, Apr 11, 2024 at 09:11:20PM -0700, Charlie Jenkins wrote:
> > Ensure that hwprobe does not flag "v" when xtheadvector is present.
> >
> > Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> > ---
> >  arch/riscv/kernel/sys_hwprobe.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> > index 8cae41a502dd..e0a42c851511 100644
> > --- a/arch/riscv/kernel/sys_hwprobe.c
> > +++ b/arch/riscv/kernel/sys_hwprobe.c
> > @@ -69,7 +69,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
> >       if (riscv_isa_extension_available(NULL, c))
> >               pair->value |= RISCV_HWPROBE_IMA_C;
> >
> > -     if (has_vector())
> > +     if (has_vector() && !riscv_has_vendor_extension_unlikely(RISCV_ISA_VENDOR_EXT_XTHEADVECTOR))
>
> Hmm, I think this is "dangerous". has_vector() is used across the kernel
> now in several places for the in-kernel vector. I don't think that
> has_vector() should return true for the T-Head stuff given that &
> has_vector() should represent the ratified spec. I'll have to think
> about this one and how nasty this makes any of the save/restore code
> etc.

Yeah, my nose crinkled here as well. If you're having to do a
vendorish thing in this generic spot, then others may too, suggesting
perhaps this isn't the cleanest way to go about it. Ideally extensions
are all additive, rather than subtractive, I guess?


>
> >               pair->value |= RISCV_HWPROBE_IMA_V;
> >
> >       /*
> > @@ -112,7 +112,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
> >               EXT_KEY(ZACAS);
> >               EXT_KEY(ZICOND);
> >
> > -             if (has_vector()) {
> > +             if (has_vector() && !riscv_has_vendor_extension_unlikely(RISCV_ISA_VENDOR_EXT_XTHEADVECTOR)) {
> >                       EXT_KEY(ZVBB);
> >                       EXT_KEY(ZVBC);
> >                       EXT_KEY(ZVKB);
> >
> > --
> > 2.44.0
> >