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Commit 5c137714 authored by Suzuki K Poulose's avatar Suzuki K Poulose Committed by Will Deacon
Browse files

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: default avatarDave Martin <dave.martin@arm.com>
Signed-off-by: default avatarSuzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent ed478b3f

arch/arm64/include/asm/cpufeature.h

+8 −0
Original line number Diff line number Diff line
@@ -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;

arch/arm64/kernel/cpufeature.c

+1 −1
Original line number Diff line number Diff line
@@ -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