[PATCH v2 09/20] arm64: capabilities: Introduce weak features based on local CPU
From: suzuki.poulose@arm.com (Suzuki K Poulose)
Date: 2018-01-31 18:29:02
Also in:
lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
Now that we have the flexibility of defining system features based on individual CPUs, introduce CPU feature type that can be detected on a local SCOPE and ignores the conflict on late CPUs. This is applicable for ARM64_HAS_NO_HW_PREFETCH, where it is fine for the system to have CPUs without hardware prefetch turning up later. We only suffer a performance penalty, nothing fatal. Cc: Will Deacon <redacted> Cc: Dave Martin <dave.martin@arm.com> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> --- arch/arm64/include/asm/cpufeature.h | 8 ++++++++ arch/arm64/kernel/cpufeature.c | 2 +- 2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index cda62b70d338..7bb3fdec827e 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h@@ -214,6 +214,14 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; */ #define ARM64_CPUCAP_SYSTEM_FEATURE \ (ARM64_CPUCAP_SCOPE_SYSTEM | ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU) +/* + * CPU feature detected at boot time based on feature of one or more CPUs. + * All possible conflicts for a late CPU are ignored. + */ +#define ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE \ + (ARM64_CPUCAP_SCOPE_LOCAL_CPU | \ + ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU | \ + ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU) struct arm64_cpu_capabilities { const char *desc;
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index c710ef28524e..ecc87aa74c64 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c@@ -956,7 +956,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = { { .desc = "Software prefetching using PRFM", .capability = ARM64_HAS_NO_HW_PREFETCH, - .type = ARM64_CPUCAP_SYSTEM_FEATURE, + .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, .matches = has_no_hw_prefetch, }, #ifdef CONFIG_ARM64_UAO
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2.14.3