linux-kernel - Re: [PATCH v3 2/9] arm64/sysreg: Update ID_AA64ISAR3

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Message-ID: <20241219155547.GC24724@willie-the-truck>
Date: Thu, 19 Dec 2024 15:55:48 +0000
From: Will Deacon <will@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Shuah Khan <shuah@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 2/9] arm64/sysreg: Update ID_AA64ISAR3_EL1 to DDI0601
 2024-09

On Thu, Dec 12, 2024 at 11:33:05AM +0000, Mark Brown wrote:
> On Wed, Dec 11, 2024 at 10:40:15PM +0000, Will Deacon wrote:
> > On Tue, Dec 10, 2024 at 06:43:05PM +0000, Mark Brown wrote:
> 
> > > Yes, the issues here are not technical ones.  Though there are some
> > > complications -  eg, IIRC the XML doesn't encode the signedness of
> > > fields like we do and there's areas where we've deliberately diverged.
> > > Given the amount of review I end up having to do of sysreg changes your
> > > reasoning is especially apparent to me.  I've passed this feedback on
> > > (again).
> 
> > One thing we _could_ do is have a tool (in-tree) that takes two copies
> > of the sysreg file (i.e. before and after applying a diff) along with a
> > copy of the XML and, for the the new fields being added, shows how the
> > XML represents those compared to the diff. It should then be relatively
> > straightforward to flag the use of an unallocated encoding (like we had
> > here) and also things like assigning a field name to a RES0 region.
> 
> > So this wouldn't be generating the patches from the XML, but more like
> > using the XML as an oracle in a linter.
> 
> That'd be useful, yes - unfortunately I think that's still something I
> can't work on myself at the moment for the above mentioned non-technical
> reasons.

Is anybody able to work on it? Without insight into the "non-technical
reasons", I don't know what I'm supposed to do other than write the tool
myself (which means finding some spare cycles...) or refusing to take
wholesale sysreg definitions until it's been ironed out :/

Will