arm64: kernel: Add cpuid_feature_extract_field() for 4bit sign extension

Based on arch/arm/include/asm/cputype.h, this function does the
shifting and sign extension necessary when accessing cpu feature fields.

Signed-off-by: James Morse <james.morse@arm.com>
Suggested-by: Russell King <linux@arm.linux.org.uk>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index c1044218a63a..9fafa7537997 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -70,6 +70,13 @@ static inline void cpus_set_cap(unsigned int num)
 		__set_bit(num, cpu_hwcaps);
 }
 
+static inline int __attribute_const__ cpuid_feature_extract_field(u64 features,
+								  int field)
+{
+	return (s64)(features << (64 - 4 - field)) >> (64 - 4);
+}
+
+
 void check_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
 			    const char *info);
 void check_local_cpu_errata(void);