linux-kernel - Re: [PATCH] arm64: cpufeature: Export Armv8.6 Matrix feature to userspace

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Date:   Tue, 29 Oct 2019 11:36:07 +0000
From:   Will Deacon <will@...nel.org>
To:     Julien Grall <julien.grall@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, suzuki.poulose@....com,
        Dave.Martin@....com
Subject: Re: [PATCH] arm64: cpufeature: Export Armv8.6 Matrix feature to
 userspace

On Tue, Oct 29, 2019 at 11:26:41AM +0000, Julien Grall wrote:
> On 29/10/2019 11:15, Will Deacon wrote:
> > On Fri, Oct 25, 2019 at 06:10:56PM +0100, Julien Grall wrote:
> > > This patch provides support for reporting the presence of Armv8.6
> > > Matrix and its optional features to userspace.
> > 
> > Are you sure this is 8.6 and not earlier?
> 
> This was introduced by Armv8.6 see [1] but allowed to be used by Armv8.2 and
> onwards.

That doesn't mean an awful lot though, especially then the features are
referred to in the docs as things like "ARMv8.2-F64MM".

> > > @@ -227,6 +229,12 @@ infrastructure:
> > >        +------------------------------+---------+---------+
> > >        | Name                         |  bits   | visible |
> > >        +------------------------------+---------+---------+
> > > +     | F64MM                        | [56-59] |    y    |
> > > +     +------------------------------+---------+---------+
> > > +     | F32MM                        | [52-55] |    y    |
> > > +     +------------------------------+---------+---------+
> > > +     | I8MM                         | [44-47] |    y    |
> > > +     +------------------------------+---------+---------+
> > 
> > Urgh, we're inconsistent in our bitfields. Some are [lo-hi] whilst others
> > are [hi-lo]. Please can you fix that in a preparatory patch? I prefer
> > [hi-lo] and it matches the arch docs.
> 
> Sure.

Thanks.

Will