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Date: Wed, 1 May 2024 10:04:58 -0700
From: Charlie Jenkins <charlie@rivosinc.com>
To: Conor Dooley <conor@kernel.org>
Cc: 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>,
	Conor Dooley <conor.dooley@microchip.com>,
	Evan Green <evan@rivosinc.com>,
	=?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 v4 05/16] riscv: Extend cpufeature.c to detect vendor
 extensions
Message-ID: <ZjJ2Omhynz02mAGk@ghost>
References: <20240426-dev-charlie-support_thead_vector_6_9-v4-0-b692f3c516ec@rivosinc.com>
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 <20240501-chastise-gecko-342f2c35cfc1@spud>
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In-Reply-To: <20240501-chastise-gecko-342f2c35cfc1@spud>

On Wed, May 01, 2024 at 11:46:07AM +0100, Conor Dooley wrote:
> On Fri, Apr 26, 2024 at 02:29:19PM -0700, Charlie Jenkins wrote:
> > Separate vendor extensions out into one struct per vendor
> > instead of adding vendor extensions onto riscv_isa_ext.
> > 
> > Add a hidden config RISCV_ISA_VENDOR_EXT to conditionally include this
> > code.
> > 
> > The xtheadvector vendor extension is added using these changes.
> 
> This mostly looks good to me, thanks for the updates. There's one thing
> that I think is wrong, but I need to test and will get back to you on...
> 
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > ---
> >  arch/riscv/Kconfig                               |  2 +
> >  arch/riscv/Kconfig.vendor                        | 19 ++++++
> >  arch/riscv/include/asm/cpufeature.h              | 18 ++++++
> >  arch/riscv/include/asm/vendor_extensions.h       | 26 ++++++++
> >  arch/riscv/include/asm/vendor_extensions/thead.h | 19 ++++++
> >  arch/riscv/kernel/Makefile                       |  2 +
> >  arch/riscv/kernel/cpufeature.c                   | 77 ++++++++++++++++++------
> >  arch/riscv/kernel/vendor_extensions.c            | 18 ++++++
> >  arch/riscv/kernel/vendor_extensions/Makefile     |  3 +
> >  arch/riscv/kernel/vendor_extensions/thead.c      | 36 +++++++++++
> >  10 files changed, 200 insertions(+), 20 deletions(-)
> > 
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index be09c8836d56..fec86fba3acd 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -759,6 +759,8 @@ config RISCV_EFFICIENT_UNALIGNED_ACCESS
> >  
> >  endchoice
> >  
> > +source "arch/riscv/Kconfig.vendor"
> > +
> >  endmenu # "Platform type"
> >  
> >  menu "Kernel features"
> > diff --git a/arch/riscv/Kconfig.vendor b/arch/riscv/Kconfig.vendor
> > new file mode 100644
> > index 000000000000..4fc86810af1d
> > --- /dev/null
> > +++ b/arch/riscv/Kconfig.vendor
> > @@ -0,0 +1,19 @@
> > +menu "Vendor extensions"
> > +
> > +config RISCV_ISA_VENDOR_EXT
> > +	bool
> > +
> > +menu "T-Head"
> > +config RISCV_ISA_VENDOR_EXT_THEAD
> > +	bool "T-Head vendor extension support"
> > +	select RISCV_ISA_VENDOR_EXT
> > +	default y
> > +	help
> > +	  Say N here if you want to disable all T-Head vendor extension
> > +	  support. This will cause any T-Head vendor extensions that are
> > +	  requested to be ignored.
> 
> What does "requested to be ignored" mean to a punter configuring a
> kernel? I'd expect this to be something like:
> 
> "Say N here to disable detection of and support for all T-Head vendor
> extensions. Without this option enabled, T-Head vendor extensions will
> not be detected at boot and their presence not reported to userspace."

Sounds great I will change to that.

- Charlie

> 
> In general, I'd expect something that needs some support in the kernel
> (like vector) to function to have a dedicated option, but the likes of
> their Zba variant could be detected and reported via hwprobe et al
> once RISCV_ISA_VENDOR_EXT_THEAD is enabled.
> 
> Cheers,
> Conor.