linux-kernel - [PATCH] perf: Change PMCR write to read-modify-write

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Date:   Wed, 20 Mar 2019 19:07:46 -0700
From:   Prasad Sodagudi <psodagud@...eaurora.org>
To:     will.deacon@....com, mingo@...hat.com, catalin.marinas@....com,
        linux-arm-kernel@...ts.infradead.org, peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, psodagud@...eaurora.org
Subject: [PATCH] perf: Change PMCR write to read-modify-write

Preserves the bitfields of PMCR_EL0(AArch64) during PMU reset.
Reset routine should write a 1 to PMCR.C and PMCR.P fields only
to reset the counters. Other fields should not be changed
as they could be set before PMU initialization and their
value must be preserved even after reset.

Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
---
 arch/arm64/kernel/perf_event.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 4addb38..0c1afdd 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -868,8 +868,8 @@ static void armv8pmu_reset(void *info)
 	 * Initialize & Reset PMNC. Request overflow interrupt for
 	 * 64 bit cycle counter but cheat in armv8pmu_write_counter().
 	 */
-	armv8pmu_pmcr_write(ARMV8_PMU_PMCR_P | ARMV8_PMU_PMCR_C |
-			    ARMV8_PMU_PMCR_LC);
+	armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_P |
+			ARMV8_PMU_PMCR_C | ARMV8_PMU_PMCR_LC);
 }
 
 static int __armv8_pmuv3_map_event(struct perf_event *event,
-- 
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