linux-kernel - Re: [PATCH v3 1/8] RISC-V: Add Zicclsm to cpufeature and hwprobe

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Date: Wed, 26 Jun 2024 15:41:19 +0100
From: Conor Dooley <conor@...nel.org>
To: Jesse Taube <jesse@...osinc.com>
Cc: linux-riscv@...ts.infradead.org, Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Clément Léger <cleger@...osinc.com>,
	Evan Green <evan@...osinc.com>,
	Andrew Jones <ajones@...tanamicro.com>,
	Charlie Jenkins <charlie@...osinc.com>,
	Xiao Wang <xiao.w.wang@...el.com>, Andy Chiu <andy.chiu@...ive.com>,
	Eric Biggers <ebiggers@...gle.com>,
	Greentime Hu <greentime.hu@...ive.com>,
	Björn Töpel <bjorn@...osinc.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Costa Shulyupin <costa.shul@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Anup Patel <apatel@...tanamicro.com>,
	Zong Li <zong.li@...ive.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Erick Archer <erick.archer@....com>,
	Joel Granados <j.granados@...sung.com>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH v3 1/8] RISC-V: Add Zicclsm to cpufeature and hwprobe

On Mon, Jun 24, 2024 at 08:49:54PM -0400, Jesse Taube wrote:
> > Zicclsm Misaligned loads and stores to main memory regions with both
> > the cacheability and coherence PMAs must be supported.
> > Note:
> > This introduces a new extension name for this feature.
> > This requires misaligned support for all regular load and store
> > instructions (including scalar and vector) but not AMOs or other
> > specialized forms of memory access. Even though mandated, misaligned
> > loads and stores might execute extremely slowly. Standard software
> > distributions should assume their existence only for correctness,
> > not for performance.
> 
> Detecing zicclsm allows the kernel to report if the
> hardware supports misaligned accesses even if support wasn't probed.
> 
> This is useful for usermode to know if vector misaligned accesses are
> supported.
> 
> Signed-off-by: Jesse Taube <jesse@...osinc.com>
> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> Reviewed-by: Andy Chiu <andy.chiu@...ive.com>
> ---
> V1 -> V2:
>  - Add documentation for Zicclsm
>  - Move Zicclsm to correct location
> V2 -> V3:
>  - No changes
> ---
>  Documentation/arch/riscv/hwprobe.rst  | 3 +++
>  arch/riscv/include/asm/hwcap.h        | 1 +
>  arch/riscv/include/uapi/asm/hwprobe.h | 1 +
>  arch/riscv/kernel/cpufeature.c        | 1 +
>  arch/riscv/kernel/sys_hwprobe.c       | 1 +
>  5 files changed, 7 insertions(+)
> 
> diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> index df5045103e73..7085a694b801 100644
> --- a/Documentation/arch/riscv/hwprobe.rst
> +++ b/Documentation/arch/riscv/hwprobe.rst
> @@ -207,6 +207,9 @@ The following keys are defined:
>    * :c:macro:`RISCV_HWPROBE_EXT_ZVE64D`: The Vector sub-extension Zve64d is
>      supported, as defined by version 1.0 of the RISC-V Vector extension manual.
>  
> +  * :c:macro:`RISCV_HWPROBE_EXT_ZICCLSM`: The Zicclsm extension is supported as
> +       defined in the RISC-V RVA Profiles Specification.

I'd rather that you regurgitated the definition here, these keys/values
cannot change their meaning, but RISC-V specs are not stable.

Cheers,
Conor.

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