From mboxrd@z Thu Jan 1 00:00:00 1970 From: suzuki.poulose@arm.com (Suzuki K Poulose) Date: Thu, 24 Nov 2016 13:40:04 +0000 Subject: [PATCH 4/9] arm64: cpufeature: Document the rules of safe value for features In-Reply-To: <1479994809-9081-1-git-send-email-suzuki.poulose@arm.com> References: <1479994809-9081-1-git-send-email-suzuki.poulose@arm.com> Message-ID: <1479994809-9081-5-git-send-email-suzuki.poulose@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 Signed-off-by: Suzuki K Poulose --- 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 -/* 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 */ -- 2.7.4