diff mbox series

[v4,1/3] arm64: cpufeature: Extract capped fields

Message ID 20200123115852.55595-2-andrew.murray@arm.com (mailing list archive)
State New, archived
Headers show
Series arm64: perf: Add support for ARMv8.5-PMU 64-bit counters | expand

Commit Message

Andrew Murray Jan. 23, 2020, 11:58 a.m. UTC 
When emulating ID registers there is often a need to cap the version
bits of a feature such that the guest will not use features that do
not yet exist.

Let's add a helper that extracts a field and caps the version to a
given value.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
---
 arch/arm64/include/asm/cpufeature.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 4261d55e8506..1462fd1101e3 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -447,6 +447,22 @@  cpuid_feature_extract_unsigned_field(u64 features, int field)
 	return cpuid_feature_extract_unsigned_field_width(features, field, 4);
 }
 
+static inline u64 __attribute_const__
+cpuid_feature_cap_signed_field_width(u64 features, int field, int width,
+				     s64 cap)
+{
+	s64 val = cpuid_feature_extract_signed_field_width(features, field,
+							   width);
+	u64 mask = GENMASK_ULL(field + width - 1, field);
+
+	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);