arm64: capabilities: Introduce weak features based on local CPU

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 <will.deacon@arm.com>
Reviewed-by: Dave Martin <dave.martin@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index c187b92..effb1c0 100644 (file)
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -239,6 +239,14 @@ 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 d330135..a80ca94 100644 (file)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1010,7 +1010,7 @@ 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