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Message-Id: <20231013024354.1289070-1-anshuman.khandual@arm.com>
Date: Fri, 13 Oct 2023 08:13:54 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Anshuman Khandual <anshuman.khandual@....com>,
Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>,
linux-kernel@...r.kernel.org, James Clark <james.clark@....com>
Subject: [PATCH V2] drivers: perf: arm_pmuv3: Read PMMIR_EL1 unconditionally
Currently the PMUv3 driver only reads PMMIR_EL1 if the PMU implements
FEAT_PMUv3p4 and the STALL_SLOT event, but the check for STALL_SLOT event
isn't necessary and can be removed.
The check for STALL_SLOT event was introduced with the read of PMMIR_EL1 in
commit f5be3a61fdb5dd11 ("arm64: perf: Add support caps under sysfs")
When this logic was written, the ARM ARM said:
| If STALL_SLOT is not implemented, it is IMPLEMENTATION DEFINED whether
| the PMMIR System registers are implemented.
... and thus the driver had to check for STALL_SLOT event to verify that
PMMIR_EL1 was implemented and accesses to PMMIR_EL1 would not be UNDEFINED.
Subsequently, the architecture was retrospectively tightened to require
that any FEAT_PMUv3p4 implementation implements PMMIR_EL1. Since the G.b
release of the ARM ARM, the wording regarding STALL_SLOT event has been
removed, and the description of PMMIR_EL1 says:
| This register is present only when FEAT_PMUv3p4 is implemented.
Drop the unnecessary check for STALL_SLOT event when reading PMMIR_EL1.
Cc: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Reviewed-by: James Clark <james.clark@....com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
This applies on v6.6-rc5
Changes in V2:
- Updated commit message to include previous context about STALL_SLOT check
Changes in V1:
https://lore.kernel.org/all/20231009075631.193208-1-anshuman.khandual@arm.com/
drivers/perf/arm_pmuv3.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index 144593092727..92fefc1bc7f6 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -1126,7 +1126,7 @@ static void __armv8pmu_probe_pmu(void *info)
pmceid, ARMV8_PMUV3_MAX_COMMON_EVENTS);
/* store PMMIR register for sysfs */
- if (is_pmuv3p4(pmuver) && (pmceid_raw[1] & BIT(31)))
+ if (is_pmuv3p4(pmuver))
cpu_pmu->reg_pmmir = read_pmmir();
else
cpu_pmu->reg_pmmir = 0;
--
2.25.1
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