[PATCH v2 4/6] arm64: kernel: Add min_register_value and use '>=' for feature detection

[James Morse]

When a new cpu feature is available, the cpu feature bits will have some
initial value, which is incremented when the feature is updated.
This patch changes 'register_value' to be 'min_register_value', and checks
the feature bits value (interpreted as a signed int) is greater than this
minimum.

Signed-off-by: James Morse <james.morse at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
---
 arch/arm64/include/asm/cpufeature.h |  4 ++--
 arch/arm64/kernel/cpufeature.c      | 14 +++++++++++---
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 7456fc44bee1..ef38e21ed719 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -42,8 +42,8 @@ struct arm64_cpu_capabilities {
 		};
 
 		struct {	/* Feature register checking */
-			u64 register_mask;
-			u64 register_value;
+			u8 register_shift;
+			u8 min_register_value;
 		};
 	};
 };
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 650ffc28bedc..cc26d6c6520b 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -23,12 +23,20 @@
 #include <asm/cpufeature.h>
 
 static bool
+feature_matches(u64 reg, const struct arm64_cpu_capabilities *entry)
+{
+	int val = cpuid_feature_extract_field(reg, entry->register_shift);
+
+	return (val >= entry->min_register_value);
+}
+
+static bool
 has_id_aa64pfr0_feature(const struct arm64_cpu_capabilities *entry)
 {
 	u64 val;
 
 	val = read_cpuid(id_aa64pfr0_el1);
-	return (val & entry->register_mask) == entry->register_value;
+	return feature_matches(val, entry);
 }
 
 static const struct arm64_cpu_capabilities arm64_features[] = {
@@ -36,8 +44,8 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.desc = "GIC system register CPU interface",
 		.capability = ARM64_HAS_SYSREG_GIC_CPUIF,
 		.matches = has_id_aa64pfr0_feature,
-		.register_mask = (0xf << 24),
-		.register_value = (1 << 24),
+		.register_shift = 24,
+		.min_register_value = 1,
 	},
 	{},
 };
-- 
2.1.4