[PATCH v5 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

[Jia He]

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 new helper cpu_has_hw_af().

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Suggested-by: Suzuki Poulose <Suzuki.Poulose@xxxxxxx>
Signed-off-by: Jia He <justin.he@xxxxxxx>
---
 arch/arm64/include/asm/cpufeature.h |  1 +
 arch/arm64/kernel/cpufeature.c      | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index c96ffa4722d3..206b6e3954cf 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -390,6 +390,7 @@ extern DECLARE_BITMAP(boot_capabilities, ARM64_NPATCHABLE);
 	for_each_set_bit(cap, cpu_hwcaps, ARM64_NCAPS)
 
 bool this_cpu_has_cap(unsigned int cap);
+bool cpu_has_hw_af(void);
 void cpu_set_feature(unsigned int num);
 bool cpu_have_feature(unsigned int num);
 unsigned long cpu_get_elf_hwcap(void);
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index b1fdc486aed8..fb0e9425d286 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1141,6 +1141,16 @@ static bool has_hw_dbm(const struct arm64_cpu_capabilities *cap,
 	return true;
 }
 
+/* Decouple AF from AFDBM. */
+bool cpu_has_hw_af(void)
+{
+	return (read_cpuid(ID_AA64MMFR1_EL1) & 0xf);
+}
+#else /* CONFIG_ARM64_HW_AFDBM */
+bool cpu_has_hw_af(void)
+{
+	return false;
+}
 #endif
 
 #ifdef CONFIG_ARM64_VHE
-- 
2.17.1