Received-SPF: pass (google.com: domain of linux-kernel+bounces-143412-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Fri, 12 Apr 2024 15:37:17 -0700
From: Charlie Jenkins <charlie@rivosinc.com>
To: Evan Green <evan@rivosinc.com>
Cc: Conor Dooley <conor.dooley@microchip.com>,
	Conor Dooley <conor@kernel.org>, Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Samuel Holland <samuel@sholland.org>,
	=?iso-8859-1?Q?Cl=E9ment_L=E9ger?= <cleger@rivosinc.com>,
	Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>,
	linux-riscv@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, Palmer Dabbelt <palmer@rivosinc.com>,
	linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
	linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 14/19] riscv: hwprobe: Disambiguate vector and
 xtheadvector in hwprobe
Message-ID: <Zhm3nflMIuue2/RS@ghost>
References: <20240411-dev-charlie-support_thead_vector_6_9-v1-0-4af9815ec746@rivosinc.com>
 <20240411-dev-charlie-support_thead_vector_6_9-v1-14-4af9815ec746@rivosinc.com>
 <20240412-moonshine-acting-0df1a90b86d2@wendy>
 <CALs-HsviR8E-sRvzz7pd5eVGb4+XsAdG1hhbZOPf+m3Cu4JP_Q@mail.gmail.com>
 <Zhl717rsQ7XLBe2F@ghost>
 <CALs-HsuL8A87mCRU2+1F2sEPYmZWTz_MFwAys0h=1uKhb7EYqg@mail.gmail.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CALs-HsuL8A87mCRU2+1F2sEPYmZWTz_MFwAys0h=1uKhb7EYqg@mail.gmail.com>

On Fri, Apr 12, 2024 at 03:08:31PM -0700, Evan Green wrote:
> On Fri, Apr 12, 2024 at 11:22 AM Charlie Jenkins <charlie@rivosinc.com> wrote:
> >
> > On Fri, Apr 12, 2024 at 10:04:42AM -0700, Evan Green wrote:
> > > 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?
> >
> > This was the "easiest" way to support this but I agree this is not
> > ideal. The vector code is naturally coupled with having support for
> > "v" and I wanted to leverage that. The other concern is all of the
> > ifdefs for having V enabled. I can make all of those V or XTHEADVECTOR;
> > that will increase the surface area of xtheadvector but it is probably
> > the right(?) way to go.
> 
> For the ifdefs, if you've got a Kconfig somewhere for THEAD_VECTOR,
> can't that just depend on the V config? We'd end up with the
> limitation that you can't add V 0.7 support without also dragging in
> V1.0 support, but that's probably fine, right?

That's a great idea, thank you for the suggestion.

- Charlie

> 
> -Evan