linux-kernel - Re: AMU extension v1 support for cortex A76, A77, A78 CPUs

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Date:   Fri, 20 Nov 2020 09:09:00 +0000
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     Marc Zyngier <maz@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>
Cc:     mark.rutland@....com, suzuki.poulose@....com,
        ionela.voinescu@....com, MSM <linux-arm-msm@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>, catalin.marinas@....com,
        Will Deacon <will@...nel.org>, valentin.schneider@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: AMU extension v1 support for cortex A76, A77, A78 CPUs

On 11/20/20 8:56 AM, Marc Zyngier wrote:
> On 2020-11-20 04:30, Neeraj Upadhyay wrote:
>> Hi,
>>
>> For ARM cortex A76, A77, A78 cores (which as per TRM, support AMU)
>> AA64PFR0[47:44] field is not set, and AMU does not get enabled for
>> them.
>> Can you please provide support for these CPUs in cpufeature.c?
> 
> If that was the case, that'd be an erratum, and it would need to be
> documented as such. It could also be that this is an optional feature
> for these cores (though the TRM doesn't suggest that).
> 
> Can someone at ARM confirm what is the expected behaviour of these CPUs?

Not a confirmation, but IIRC, these are imp def features, while our cpufeatures
catches architected one.

Cheers
Vladimir

> 
>         M.