Messages in this thread | | | Subject | Re: [PATCH 09/16] arm64: capabilities: Introduce strict features based on local CPU | From | Suzuki K Poulose <> | Date | Tue, 30 Jan 2018 11:25:51 +0000 |
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On 26/01/18 12:12, Dave Martin wrote: > On Tue, Jan 23, 2018 at 12:28:02PM +0000, Suzuki K Poulose wrote: >> Add type for features that are detected on individual CPUs, >> rather than on a system wide safe features. This behavior > > feature > >> is similar to that of a strict cpu erratum, where a later >> CPU is not allowed to boot if the system doesn't posses it. >> >> Use this for software prefetching capability. >> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> --- >> arch/arm64/include/asm/cpufeature.h | 7 +++++++ >> arch/arm64/kernel/cpufeature.c | 2 +- >> 2 files changed, 8 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h >> index a621d2184227..4c3d6987acfc 100644 >> --- a/arch/arm64/include/asm/cpufeature.h >> +++ b/arch/arm64/include/asm/cpufeature.h >> @@ -118,6 +118,13 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; >> */ >> #define ARM64_CPUCAP_BOOT_SYSTEM_FEATURE \ >> (ARM64_CPUCAP_SCOPE_SYSTEM | ARM64_CPUCAP_LATE_CPU_SAFE_TO_HAVE) >> +/* >> + * CPU feature detected at boot time based on feature of one or more CPUs. >> + * It is not safe for a late CPU to have this feature, when the system doesn't >> + * have it. But it is safe to miss the feature if the system has it. >> + */ >> +#define ARM64_CPUCAP_STRICT_CPU_LOCAL_FEATURE \ >> + (ARM64_CPUCAP_SCOPE_LOCAL_CPU | ARM64_CPUCAP_LATE_CPU_SAFE_TO_MISS) > > "STRICT" seem quite odd here, since we never require all CPUs to have > the feature. The case we forbid is when the boot-time decision is that > the system doesn't tolerate this feature. So this feels erratum-like. > >> struct arm64_cpu_capabilities { >> const char *desc; >> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >> index 7ae5cf9092d0..111f6c4b4cd7 100644 >> --- a/arch/arm64/kernel/cpufeature.c >> +++ b/arch/arm64/kernel/cpufeature.c >> @@ -951,7 +951,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = { >> { >> .desc = "Software prefetching using PRFM", >> .capability = ARM64_HAS_NO_HW_PREFETCH, >> - .type = ARM64_CPUCAP_BOOT_SYSTEM_FEATURE, >> + .type = ARM64_CPUCAP_STRICT_CPU_LOCAL_FEATURE, >> .matches = has_no_hw_prefetch, > > For ARM64_HAS_NO_HW_PREFETCH this is more describing an implementation > option that only affects performance -- in that case it's not obvious > that we should be strict at all. > > This suggests ARM64_CPUCAP_SCOPE_LOCAL_CPU | > ARM64_CPUCAP_LATE_CPU_SAFE_TO_HAVE | > ARM64_CPUCAP_LATE_CPU_SAFE_TO_MISS.
You're right. This is more like a WEAK feature we add for DBM. I will switch it.
Cheers Suzuki
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