[PATCH v2 2/9] perf/cxl: Clear stale event fields before reprogramming a counter

[Dave Jiang <dave.jiang@intel.com>]

cxl_pmu_event_start() ORs the event group id, event mask, edge and invert
selections into a configurable counter's config register without clearing
those fields first, and cxl_pmu_event_stop() leaves them set. Reusing a
counter for another event therefore ORs the new selection onto the old,
counting the wrong events with stale edge/invert behaviour.

Clear EVENT_GRP_ID_IDX, EVENTS, EDGE and INVERT before applying the new
values.

Fixes: 5d7107c72796 ("perf: CXL Performance Monitoring Unit driver")
Reported-by: sashiko-bot@kernel.org
Closes: https://sashiko.dev/#/patchset/20260715191454.459673-1-dave@stgolabs.net?part=1
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
 drivers/perf/cxl_pmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/perf/cxl_pmu.c b/drivers/perf/cxl_pmu.c
index e77c0650a7eb..3138514157cd 100644
--- a/drivers/perf/cxl_pmu.c
+++ b/drivers/perf/cxl_pmu.c
@@ -641,6 +641,7 @@ static void cxl_pmu_event_start(struct perf_event *event, int flags)
 	}
 
 	cfg = readq(base + CXL_PMU_COUNTER_CFG_REG(hwc->idx));
+	cfg &= ~(CXL_PMU_COUNTER_CFG_EDGE | CXL_PMU_COUNTER_CFG_INVERT);
 	cfg |= FIELD_PREP(CXL_PMU_COUNTER_CFG_INT_ON_OVRFLW, 1);
 	cfg |= FIELD_PREP(CXL_PMU_COUNTER_CFG_FREEZE_ON_OVRFLW, 1);
 	cfg |= FIELD_PREP(CXL_PMU_COUNTER_CFG_ENABLE, 1);
@@ -651,6 +652,8 @@ static void cxl_pmu_event_start(struct perf_event *event, int flags)
 
 	/* Fixed purpose counters have next two fields RO */
 	if (test_bit(hwc->idx, info->conf_counter_bm)) {
+		cfg &= ~(CXL_PMU_COUNTER_CFG_EVENT_GRP_ID_IDX_MSK |
+			 CXL_PMU_COUNTER_CFG_EVENTS_MSK);
 		cfg |= FIELD_PREP(CXL_PMU_COUNTER_CFG_EVENT_GRP_ID_IDX_MSK,
 				  hwc->event_base);
 		cfg |= FIELD_PREP(CXL_PMU_COUNTER_CFG_EVENTS_MSK,
-- 
2.55.0