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

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Message-ID: <d77713992e5abef5c6066d9f1939e8db@kernel.org>
Date:   Fri, 20 Nov 2020 09:54:48 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Vladimir Murzin <vladimir.murzin@....com>
Cc:     Neeraj Upadhyay <neeraju@...eaurora.org>, 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 2020-11-20 09:09, Vladimir Murzin wrote:
> 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.

Ah, good point. So these CPUs implement some sort of AMU, and not *the* 
AMU.

Yet the register names are the same. Who thought that'd be a good idea?

         M.
-- 
Jazz is not dead. It just smells funny...