[PATCH 1/2] perf: arm_pmuv3: Factor out PMCCNTR_EL0 use conditions

[Yicong Yang]

From: Yicong Yang <yangyicong at hisilicon.com>

PMCCNTR_EL0 is preferred for counting CPU_CYCLES under certain
conditions. Factor out the condition check to a separate function
for further extension. Add documents for better understanding.
No functional changes intended.

Signed-off-by: Yicong Yang <yangyicong at hisilicon.com>
---
 drivers/perf/arm_pmuv3.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index f6d7bab5d555..95c899d07df5 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -978,6 +978,33 @@ static int armv8pmu_get_chain_idx(struct pmu_hw_events *cpuc,
 	return -EAGAIN;
 }
 
+static bool armv8pmu_can_use_pmccntr(struct pmu_hw_events *cpuc,
+				     struct perf_event *event)
+{
+	struct hw_perf_event *hwc = &event->hw;
+	unsigned long evtype = hwc->config_base & ARMV8_PMU_EVTYPE_EVENT;
+
+	/* PMCCNTR_EL0 can only be used for CPU_CYCLES event */
+	if (evtype != ARMV8_PMUV3_PERFCTR_CPU_CYCLES)
+		return false;
+
+	/*
+	 * A CPU_CYCLES event with threshold counting cannot use PMCCNTR_EL0
+	 * since it lacks threshold support.
+	 */
+	if (armv8pmu_event_get_threshold(&event->attr))
+		return false;
+
+	/*
+	 * PMCCNTR_EL0 is not affected by BRBE controls like BRBCR_ELx.FZP.
+	 * So don't use it for branch events.
+	 */
+	if (has_branch_stack(event))
+		return false;
+
+	return true;
+}
+
 static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 				  struct perf_event *event)
 {
@@ -986,8 +1013,7 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 	unsigned long evtype = hwc->config_base & ARMV8_PMU_EVTYPE_EVENT;
 
 	/* Always prefer to place a cycle counter into the cycle counter. */
-	if ((evtype == ARMV8_PMUV3_PERFCTR_CPU_CYCLES) &&
-	    !armv8pmu_event_get_threshold(&event->attr) && !has_branch_stack(event)) {
+	if (armv8pmu_can_use_pmccntr(cpuc, event)) {
 		if (!test_and_set_bit(ARMV8_PMU_CYCLE_IDX, cpuc->used_mask))
 			return ARMV8_PMU_CYCLE_IDX;
 		else if (armv8pmu_event_is_64bit(event) &&
-- 
2.24.0