linux-kernel - Re: [PATCH 9/9] arm64: Documentation

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Message-ID: <20161130113150.GB4439@e104818-lin.cambridge.arm.com>
Date:   Wed, 30 Nov 2016 11:31:50 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Siddhesh Poyarekar <sid@...erved-bit.com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, mark.rutland@....com,
        ryan.arnold@...aro.org, aph@...hat.com, will.deacon@....com,
        linux-kernel@...r.kernel.org, marc.zyngier@....com,
        adhemerval.zanella@...aro.org, dave.martin@....com
Subject: Re: [PATCH 9/9] arm64: Documentation - Expose CPU feature registers

On Wed, Nov 30, 2016 at 04:44:52PM +0530, Siddhesh Poyarekar wrote:
> On Thursday 24 November 2016 07:10 PM, Suzuki K Poulose wrote:
> > + d) CPU Identification :
> > +    MIDR_EL1 is exposed to help identify the processor. On a
> > +    heterogeneous system, this could be racy (just like getcpu()). The
> > +    process could be migrated to another CPU by the time it uses the
> > +    register value, unless the CPU affinity is set. Hence, there is no
> > +    guarantee that the value reflects the processor that it is
> > +    currently executing on. The REVIDR is not exposed due to this
> > +    constraint, as REVIDR makes sense only in conjunction with the
> > +    MIDR. Alternately, MIDR_EL1 and REVIDR_EL1 are exposed via sysfs
> > +    at:
> > +
> > +	/sys/devices/system/cpu/cpu$ID/regs/identification/
> > +	                                              \- midr
> > +	                                              \- revidr
> > +
> 
> This doesn't seem to be implemented in this patchset.

No. However, we merged the functionality above already and forgot about
the documentation part, so we just clarify it now.

-- 
Catalin