From 156e0d57f8bc9a4c0f09f4f79af7b51c6d7d0600 Mon Sep 17 00:00:00 2001 From: Suzuki K Poulose Date: Mon, 9 Jan 2017 17:28:27 +0000 Subject: 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 Cc: Catalin Marinas Cc: Will Deacon Cc: Mark Rutland Reviewed-by: Catalin Marinas Signed-off-by: Suzuki K Poulose Signed-off-by: Will Deacon --- arch/arm64/include/asm/cpufeature.h | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) (limited to 'arch/arm64/include') 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 #include -/* 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 */ -- cgit v1.2.3