Messages in this thread Patch in this message | | | Date | Fri, 26 Jan 2018 12:12:20 +0000 | From | Dave Martin <> | Subject | Re: [PATCH 09/16] arm64: capabilities: Introduce strict features based on local CPU |
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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.
But IIUC it doesn't make a difference for the only real systems that this feature is relevant to.
[...]
Cheers ---Dave
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