arm64: cpufeature: introduce helper cpu_has_hw_af()

We unconditionally set the HW_AFDBM capability and only enable it on
CPUs which really have the feature. But sometimes we need to know
whether this cpu has the capability of HW AF. So decouple AF from
DBM by a new helper cpu_has_hw_af().

If later we noticed a potential performance issue on this path, we can
turn it into a static label as with other CPU features.
Signed-off-by: NJia He <justin.he@arm.com>
Suggested-by: NSuzuki Poulose <Suzuki.Poulose@arm.com>
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/cpufeature.h

@@ -659,6 +659,20 @@ static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
 	default: return CONFIG_ARM64_PA_BITS;
 	}
 }
+
+/* Check whether hardware update of the Access flag is supported */
+static inline bool cpu_has_hw_af(void)
+{
+	u64 mmfr1;
+
+	if (!IS_ENABLED(CONFIG_ARM64_HW_AFDBM))
+		return false;
+
+	mmfr1 = read_cpuid(ID_AA64MMFR1_EL1);
+	return cpuid_feature_extract_unsigned_field(mmfr1,
+						ID_AA64MMFR1_HADBS_SHIFT);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif