linux-kernel - Re: [PATCH v2 1/6] RISC-V: Add Zicclsm to cpufeature and hwprobe

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Message-ID: <20240614-oyster-ditch-80e8f00fd91b@wendy>
Date: Fri, 14 Jun 2024 09:09:15 +0100
From: Conor Dooley <conor.dooley@...rochip.com>
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>, Conor Dooley <conor@...nel.org>, 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>
Subject: Re: [PATCH v2 1/6] RISC-V: Add Zicclsm to cpufeature and hwprobe

On Thu, Jun 13, 2024 at 03:16:10PM -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>

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