diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index f63438474dd5..587b8a804fc7 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -449,6 +449,29 @@ cpuid_feature_extract_unsigned_field(u64 features, int field) return cpuid_feature_extract_unsigned_field_width(features, field, 4); } +/* + * Fields that identify the version of the Performance Monitors Extension do + * not follow the standard ID scheme. See ARM DDI 0487E.a page D13-2825, + * "Alternative ID scheme used for the Performance Monitors Extension version". + */ +static inline u64 __attribute_const__ +cpuid_feature_cap_perfmon_field(u64 features, int field, u64 cap) +{ + u64 val = cpuid_feature_extract_unsigned_field(features, field); + u64 mask = GENMASK_ULL(field + 3, field); + + /* Treat IMPLEMENTATION DEFINED functionality as unimplemented */ + if (val == 0xf) + val = 0; + + if (val > cap) { + features &= ~mask; + features |= (cap << field) & mask; + } + + return features; +} + static inline u64 arm64_ftr_mask(const struct arm64_ftr_bits *ftrp) { return (u64)GENMASK(ftrp->shift + ftrp->width - 1, ftrp->shift);