[PATCH] arm64: pmuv3: handle pmuv3+

[mark.rutland@arm.com (Mark Rutland)]

Commit f1b36dcb5c316c27 ("arm64: pmuv3: handle !PMUv3 when probing") is
a little too restrictive, and prevents the use of of backwards
compatible PMUv3 extenstions, which have a PMUver value other than 1.

For instance, ARMv8.1 PMU extensions (as implemented by ThunderX2) are
reported with PMUver value 4.

Per the usual ID register principles, at least 0x1-0x7 imply a
PMUv3-compatible PMU. It's not currently clear whether 0x8-0xe imply the
same.

For the time being, treat the value as signed, and with 0x1-0x7 treated
as meaning PMUv3 is implemented. This may be relaxed by future patches.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: Jayachandran C <jnair@caviumnetworks.com>
Cc: Will Deacon <will.deacon@arm.com>
---
 arch/arm64/kernel/perf_event.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Will, would you be happy to queue this fixup for v4.12?

Thanks,
Mark.

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 98c7493..5f64d19 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -966,13 +966,14 @@ static void __armv8pmu_probe_pmu(void *info)
 {
 	struct armv8pmu_probe_info *probe = info;
 	struct arm_pmu *cpu_pmu = probe->pmu;
-	u64 dfr0, pmuver;
+	u64 dfr0;
 	u32 pmceid[2];
+	int pmuver;
 
 	dfr0 = read_sysreg(id_aa64dfr0_el1);
-	pmuver = cpuid_feature_extract_unsigned_field(dfr0,
+	pmuver = cpuid_feature_extract_signed_field(dfr0,
 			ID_AA64DFR0_PMUVER_SHIFT);
-	if (pmuver != 1)
+	if (pmuver < 1)
 		return;
 
 	probe->present = true;
-- 
1.9.1