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

From: Suzuki K. Poulose
Date: Fri Sep 25 2015 - 09:06:00 EST

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@xxxxxxx>

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).


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