linux-kernel - Re: [PATCH 07/22] arm64: Keep track of CPU feature registers

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Message-ID: <560546B0.7070909@arm.com>
Date:	Fri, 25 Sep 2015 14:05:52 +0100
From:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
To:	Dave P Martin <Dave.Martin@....com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <Mark.Rutland@....com>,
	"ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
	"aph@...hat.com" <aph@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"edward.nevill@...aro.org" <edward.nevill@...aro.org>,
	Andre Przywara <Andre.Przywara@....com>,
	Marc Zyngier <Marc.Zyngier@....com>
Subject: Re: [PATCH 07/22] arm64: Keep track of CPU feature registers

On 25/09/15 12:38, Dave P Martin wrote:
> On Wed, Sep 16, 2015 at 03:21:05PM +0100, Suzuki K. Poulose wrote:
>> From: "Suzuki K. Poulose" <suzuki.poulose@....com>
>>
>> This patch adds an infrastructure to keep track of the CPU feature
>> registers on the system. For each register, the infrastructure keeps
>> track of the system wide safe value of the feature bits. Also, tracks
>> the which fields of a register should be matched strictly across all
>> the CPUs on the system for the SANITY check infrastructure.
>>
>> The feature bits are classified as one of SCALAR_MIN, SCALAR_MAX and DISCRETE
>> depending on the implication of the possible values. This information
>> is used to decide the safe value for a feature.
>>
>> SCALAR_MIN - The smaller value is safer
>> SCALAR_MAX - The bigger value is safer
>> DISCRETE - We can't decide between the two, so a predefined safe_value is used.
>
> Can documentation of the meanings of these be added somewhere in the
> relevant header or in Documentation?

Sure. They were part of the initial draft and eventually lost them over the
reworks. I will add them back, since there is wider use of the information
across the system, from what I started with(i.e, Userspace visibility).

Cheers
Suzuki

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