Subject: [PATCH v11 1/4] arm64: cpufeature: introduce helper cpu_has_hw_af()

From: Jia He <[email-masked]>
Date: Wed, 9 Oct 2019 16:42:43 +0800

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().

Signed-off-by: Jia He <[email-masked]>
Suggested-by: Suzuki Poulose <[email-masked]>
Reviewed-by: Catalin Marinas <[email-masked]>
---
 arch/arm64/include/asm/cpufeature.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9cde5d2e768f..1a95396ea5c8 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/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)
+{
+	if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM)) {
+		u64 mmfr1 = read_cpuid(ID_AA64MMFR1_EL1);
+
+		return !!cpuid_feature_extract_unsigned_field(mmfr1,
+						ID_AA64MMFR1_HADBS_SHIFT);
+	}
+
+	return false;
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif
-- 
2.17.1

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