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Date:   Fri, 20 Nov 2020 10:20:42 +0000
From:   Sudeep Holla <sudeep.holla@arm.com>
To:     Marc Zyngier <maz@kernel.org>
Cc:     Neeraj Upadhyay <neeraju@codeaurora.org>, mark.rutland@arm.com,
        suzuki.poulose@arm.com, ionela.voinescu@arm.com,
        MSM <linux-arm-msm@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>, catalin.marinas@arm.com,
        Will Deacon <will@kernel.org>, valentin.schneider@arm.com,
        linux-arm-kernel@lists.infradead.org
Subject: Re: AMU extension v1 support for cortex A76, A77, A78 CPUs
Message-ID: <20201120102042.25caeib3iiuxkogt@bogus>
References: <2cc9dd44-0b4b-94a8-155a-7a2446a1b892@codeaurora.org>
 <1712842eb0767e51155a5396d282102c@kernel.org>
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On Fri, Nov 20, 2020 at 08:56:31AM +0000, 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?

IIRC discussion with Ionela long back, we intentionally decided not to
support IMPDEF(pre 8.4 non-architected so called AMUs) on the CPUs listed
in $subject.

--
Regards,
Sudeep