[PATCH v3 2/2] perf/imx_ddr: don't enable counter0 if none of 4 counters

[Xu Yang]

In current driver, counter0 will be enabled after ddr_perf_pmu_enable()
is called even though none of the 4 counters are used. This will cause
counter0 continue to count until ddr_perf_pmu_disabled() is called. If
pmu is not disabled all the time, the pmu interrupt will be asserted
from time to time due to counter0 will overflow and irq handler will
clear it. It's not an expected behavior. This patch will not enable
counter0 if none of 4 counters are used.

Fixes: 9a66d36cc7ac ("drivers/perf: imx_ddr: Add DDR performance counter support to perf")
Signed-off-by: Xu Yang <xu.yang_2 at nxp.com>

---
Changes in v3:
 - don't differentiate cycle counter and other counters
 - modify logic in pmu_enable()/pmu_disable()
Changes in v2:
 - add active events count as suggested from Frank
---
 drivers/perf/fsl_imx8_ddr_perf.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/perf/fsl_imx8_ddr_perf.c b/drivers/perf/fsl_imx8_ddr_perf.c
index f8a94c051f41..32deeace2c93 100644
--- a/drivers/perf/fsl_imx8_ddr_perf.c
+++ b/drivers/perf/fsl_imx8_ddr_perf.c
@@ -103,6 +103,7 @@ struct ddr_pmu {
 	const struct fsl_ddr_devtype_data *devtype_data;
 	int irq;
 	int id;
+	int active_count;
 };
 
 static ssize_t ddr_perf_identifier_show(struct device *dev,
@@ -516,6 +517,7 @@ static void ddr_perf_event_start(struct perf_event *event, int flags)
 
 	ddr_perf_counter_enable(pmu, event->attr.config, counter, true);
 
+	pmu->active_count++;
 	hwc->state = 0;
 }
 
@@ -569,6 +571,7 @@ static void ddr_perf_event_stop(struct perf_event *event, int flags)
 	ddr_perf_counter_enable(pmu, event->attr.config, counter, false);
 	ddr_perf_event_update(event);
 
+	pmu->active_count--;
 	hwc->state |= PERF_HES_STOPPED;
 }
 
@@ -588,8 +591,11 @@ static void ddr_perf_pmu_enable(struct pmu *pmu)
 {
 	struct ddr_pmu *ddr_pmu = to_ddr_pmu(pmu);
 
-	/* enable cycle counter if cycle is not active event list */
-	if (ddr_pmu->events[EVENT_CYCLES_COUNTER] == NULL)
+	/*
+	 * Because counter 1-3 depend on cycle counter, treat cycle
+	 * counter as main switch when any counter of the 4 need to run.
+	 */
+	if (ddr_pmu->active_count > 0)
 		ddr_perf_counter_enable(ddr_pmu,
 				      EVENT_CYCLES_ID,
 				      EVENT_CYCLES_COUNTER,
@@ -600,11 +606,13 @@ static void ddr_perf_pmu_disable(struct pmu *pmu)
 {
 	struct ddr_pmu *ddr_pmu = to_ddr_pmu(pmu);
 
-	if (ddr_pmu->events[EVENT_CYCLES_COUNTER] == NULL)
-		ddr_perf_counter_enable(ddr_pmu,
-				      EVENT_CYCLES_ID,
-				      EVENT_CYCLES_COUNTER,
-				      false);
+	/*
+	 * Counting should be stopped. Disable cycle counter unconditionally.
+	 */
+	ddr_perf_counter_enable(ddr_pmu,
+			      EVENT_CYCLES_ID,
+			      EVENT_CYCLES_COUNTER,
+			      false);
 }
 
 static int ddr_perf_init(struct ddr_pmu *pmu, void __iomem *base,
-- 
2.34.1