linux-kernel - Re: [PATCH 3/3] arm64: cpuinfo: display product info in /proc/cpuinfo

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Date:   Wed, 27 Sep 2017 14:39:32 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Al Stone <ahs3@...hat.com>, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH 3/3] arm64: cpuinfo: display product info in /proc/cpuinfo

Hi,

On Wed, Sep 27, 2017 at 11:42:07AM +0100, Robin Murphy wrote:
> On 26/09/17 23:23, Al Stone wrote:
> > +			seq_printf(m, ", ARM 8.%d (r%dp%d) CPU",
> > +				   MIDR_VARIANT(midr),
> > +				   MIDR_VARIANT(midr),
> > +				   MIDR_REVISION(midr));
> 
> What is "ARM 8.1" meant to infer for, say, a typical Cortex-A57?

Just to make Robin's point a little clearer, MIDR_EL1.Variant is
IMPLEMENTATION DEFINED, and doesn't describe the ARMv8.x architecture
revision.

For example, on Cortex A57 is contains the major revision number of the
CPU, and is 1 for any r1pY Cortex-A57 (e.g. those on Juno R1).

For better or worse, the architecture provides us no mechanism to
determine the architecture revision.

Thanks,
Mark.