linux-kernel - Re: [PATCH] arm64/fpsimd: Only provide the length to cpufeature for xCR registers

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Message-ID: <371e0fb4-0f99-40cc-b93f-0eae700d720c@sirena.org.uk>
Date:   Wed, 2 Aug 2023 13:21:25 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Will Deacon <will@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Dave Martin <Dave.Martin@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/fpsimd: Only provide the length to cpufeature for
 xCR registers

On Wed, Aug 02, 2023 at 12:21:23PM +0100, Will Deacon wrote:
> On Thu, Jul 27, 2023 at 10:31:44PM +0100, Mark Brown wrote:

> > -	return zcr;
> > +	return SYS_FIELD_GET(ZCR_ELx, LEN, zcr);

> Hmm, now this function looks like a mixture of code which relies on the
> LEN field living at the bottom of the register and code which is agnostic
> to that.

> Can we update the 'zcr |= vq_max - 1' part to use something like
> FIELD_PREP() instead?

There was a version 2 that was sent already which goes in the opposite
direction and just returns the value we would munge in without use of
any FIELD_ macros:

   https://lore.kernel.org/r/20230731-arm64-sme-fa64-hotplug-v2-1

which also addresses your issue?

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