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.poul...@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
