linux-kernel - [PATCH] perf: arm_pmuv3: Avoid assigning fixed cycle counter with threshold

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Date: Tue, 11 Jun 2024 09:50:12 -0600
From: "Rob Herring (Arm)" <robh@...nel.org>
To: Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	James Clark <james.clark@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] perf: arm_pmuv3: Avoid assigning fixed cycle counter with threshold

If the user has requested a counting threshold for the CPU cycles event,
then the fixed cycle counter can't be assigned as it lacks threshold
support. Currently, the thresholds will work or not randomly depending
on which counter the event is assigned.

While using thresholds for CPU cycles doesn't make much sense, it can be
useful for testing purposes.

Fixes: 816c26754447 ("arm64: perf: Add support for event counting threshold")
Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
---
 drivers/perf/arm_pmuv3.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index 23fa6c5da82c..2612be29ee23 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -939,9 +939,10 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
 	struct hw_perf_event *hwc = &event->hw;
 	unsigned long evtype = hwc->config_base & ARMV8_PMU_EVTYPE_EVENT;
+	bool has_threshold = !!(hwc->config_base & ARMV8_PMU_EVTYPE_TH);
 
 	/* Always prefer to place a cycle counter into the cycle counter. */
-	if (evtype == ARMV8_PMUV3_PERFCTR_CPU_CYCLES) {
+	if ((evtype == ARMV8_PMUV3_PERFCTR_CPU_CYCLES) && !has_threshold) {
 		if (!test_and_set_bit(ARMV8_IDX_CYCLE_COUNTER, cpuc->used_mask))
 			return ARMV8_IDX_CYCLE_COUNTER;
 		else if (armv8pmu_event_is_64bit(event) &&
-- 
2.43.0