linux-kernel - Re: [PATCH] arm64/sysreg: Update ID_AA64MMFR2

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Date: Mon, 22 Apr 2024 18:16:13 +0100
From: Will Deacon <will@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
	Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/sysreg: Update ID_AA64MMFR2_EL1 register

On Mon, Apr 22, 2024 at 08:38:40AM +0530, Anshuman Khandual wrote:
> 
> 
> On 4/19/24 19:16, Will Deacon wrote:
> > On Fri, Apr 19, 2024 at 07:43:25AM +0530, Anshuman Khandual wrote:
> >> This updates ID_AA64MMFR2_EL1.VARange register fields as per the definition
> >> based on DDI0601 2024-03.
> >>
> >> Cc: Catalin Marinas <catalin.marinas@....com>
> >> Cc: Will Deacon <will@...nel.org>
> >> Cc: Mark Brown <broonie@...nel.org>
> >> Cc: linux-arm-kernel@...ts.infradead.org
> >> Cc: linux-kernel@...r.kernel.org
> >> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> >> ---
> >> This applies on v6.9-rc4
> >>
> >>  arch/arm64/tools/sysreg | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> >> index a4c1dd4741a4..6d7213dcbeb5 100644
> >> --- a/arch/arm64/tools/sysreg
> >> +++ b/arch/arm64/tools/sysreg
> >> @@ -1739,6 +1739,7 @@ EndEnum
> >>  UnsignedEnum	19:16	VARange
> >>  	0b0000	48
> >>  	0b0001	52
> >> +	0b0010	56
> > 
> > Is anybody using this? I'm not sure there's a lot of value in adding
> > these fields one-by-one for the sake of completeness.
> 
> This is not being used currently but will be required for upcoming
> features. I was under the impression that register fields (atleast
> for the ID registers) should be kept updated, with latest released
> spec ? Besides lately arch/arm64/tools/sysreg serves as very good
> reference for all necessary register fields.

Why? The linux headers aren't documenting the architecture.

Will