[PATCH 4/9] arm64: cpufeature: Document the rules of safe value for features
From: suzuki.poulose@arm.com (Suzuki K Poulose)
Date: 2016-11-24 13:42:54
Also in:
lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
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 <redacted> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> --- arch/arm64/include/asm/cpufeature.h | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 0bc0b1d..59508a9 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h@@ -29,7 +29,21 @@ #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. + * + * a) LOWER_SAFE - The value 'n+1' indicates, value 'n' and some + * additional features. (where n >= 0). The smaller value (n) is + * considered safer in this case. + * b) HIGHER_SAFE - The value 'n+1' is safer than 'n' (for n>= 0). + * c) EXACT - If the values of the feature don't have any relationship, + * a predefined safe value is used. + */ + enum ftr_type { FTR_EXACT, /* Use a predefined safe value */ FTR_LOWER_SAFE, /* Smaller value is safe */
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2.7.4