linux-kernel - Re: [PATCH v4] arm64: cpuinfo: Expose MIDR_EL1 and REVIDR

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Date:	Mon, 13 Jun 2016 18:21:40 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Suzuki K Poulose <suzuki.poulose@....com>
Cc:	catalin.marinas@....com, will.deacon@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	steve.capper@....com, Steve Capper <steve.capper@...aro.org>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v4] arm64: cpuinfo: Expose MIDR_EL1 and REVIDR_EL1 to
 sysfs

On Mon, Jun 13, 2016 at 06:08:09PM +0100, Suzuki K Poulose wrote:
> From: Steve Capper <steve.capper@...aro.org>
> 
> It can be useful for JIT software to be aware of MIDR_EL1 and
> REVIDR_EL1 to ascertain the presence of any core errata that could
> affect codegen.
> 
> This patch exposes these registers through sysfs:
> 
> /sys/devices/system/cpu/cpu$ID/identification/midr
> /sys/devices/system/cpu/cpu$ID/identification/revidr
> 
> where $ID is the cpu number. For big.LITTLE systems, one can have a
> mixture of cores (e.g. Cortex A53 and Cortex A57), thus all CPUs need
> to be enumerated.
> 
> If the kernel does not have valid information to populate these entries
> with, an empty string is returned to userspace.

So there's no confusion, I've historically said no on 32-bit ARM to
exposing the MIDR to userspace, and my position on that for 32-bit
ARM has not changed.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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