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| author | Suzuki K Poulose <suzuki.poulose@arm.com> | 2017-01-09 20:28:27 +0300 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2017-01-10 20:11:23 +0300 |
| commit | 156e0d57f8bc9a4c0f09f4f79af7b51c6d7d0600 (patch) | |
| tree | 951d3db5d65ca2e46dd510d912d539633511b449 /arch/arm64 | |
| parent | eab43e88734f4ef8cb5ec40827bf784400ed8ffc (diff) | |
| download | linux-156e0d57f8bc9a4c0f09f4f79af7b51c6d7d0600.tar.xz | |
arm64: cpufeature: Document the rules of safe value for features
Document the rules for choosing the safe value for different types
of features.
Cc: Dave Martin <dave.martin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64')
| -rw-r--r-- | arch/arm64/include/asm/cpufeature.h | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index b4989df48670..10d56242e649 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -29,7 +29,20 @@ #include <linux/jump_label.h> #include <linux/kernel.h> -/* CPU feature register tracking */ +/* + * CPU feature register tracking + * + * The safe value of a CPUID feature field is dependent on the implications + * of the values assigned to it by the architecture. Based on the relationship + * between the values, the features are classified into 3 types - LOWER_SAFE, + * HIGHER_SAFE and EXACT. + * + * The lowest value of all the CPUs is chosen for LOWER_SAFE and highest + * for HIGHER_SAFE. It is expected that all CPUs have the same value for + * a field when EXACT is specified, failing which, the safe value specified + * in the table is chosen. + */ + enum ftr_type { FTR_EXACT, /* Use a predefined safe value */ FTR_LOWER_SAFE, /* Smaller value is safe */ |