From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Mon, 9 Jan 2017 12:04:35 +0000 Subject: [PATCH v3 4/9] arm64: cpufeature: Document the rules of safe value for features In-Reply-To: <2338875a-6a5b-ba9e-59fe-d681091c2923@arm.com> References: <1483552147-9605-1-git-send-email-suzuki.poulose@arm.com> <1483552147-9605-5-git-send-email-suzuki.poulose@arm.com> <20170106123011.GB12863@e104818-lin.cambridge.arm.com> <2338875a-6a5b-ba9e-59fe-d681091c2923@arm.com> Message-ID: <20170109120434.GA7593@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jan 09, 2017 at 10:43:07AM +0000, Suzuki K. Poulose wrote: > On 06/01/17 12:30, Catalin Marinas wrote: > >On Wed, Jan 04, 2017 at 05:49:02PM +0000, Suzuki K. Poulose wrote: > >>--- a/arch/arm64/include/asm/cpufeature.h > >>+++ b/arch/arm64/include/asm/cpufeature.h > >>@@ -29,7 +29,21 @@ > >> #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. > >>+ * > >>+ * 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. > >>+ */ > > > >I don't think this text fully describes what is actually compared. You > >could say something that the lowest value of all the CPUs is chosen for > >LOWER_SAFE, highest for HIGHER_SAFE and it is expected that all CPUs > >have the same value for a field when EXACT is specified. > > Ok. I have changed it as below : > > /* > * 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. > */ It looks better to me. Thanks. Reviewed-by: Catalin Marinas