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

Evan Green
2024-04-12T17:05:36Z

On Fri, Apr 12, 2024 at 4:35 AM Conor Dooley <conor.dooley@microchip.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@rivosinc.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