perf/arm-cmn: Reset DTM_PMU_CONFIG at probe

Although we treat the DTM counters as free-running such that we're not
too concerned about the initial DTM state, it's possible for a previous
user to have left DTM counters enabled and paired with DTC counters.
Thus if the first events are scheduled using some, but not all, DTMs,
the as-yet-unused ones could end up adding spurious increments to the
event counts at the DTC. Make sure we sync our initial DTM_PMU_CONFIG
state to all the DTMs at probe time to avoid that possibility.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/ba5f38b3dc733cd06bfb5e659b697e76d18c2183.1670269572.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm-cmn.c

@@ -1865,6 +1865,7 @@ static void arm_cmn_init_dtm(struct arm_cmn_dtm *dtm, struct arm_cmn_node *xp, i
 
 	dtm->base = xp->pmu_base + CMN_DTM_OFFSET(idx);
 	dtm->pmu_config_low = CMN_DTM_PMU_CONFIG_PMU_EN;
+	writeq_relaxed(dtm->pmu_config_low, dtm->base + CMN_DTM_PMU_CONFIG);
 	for (i = 0; i < 4; i++) {
 		dtm->wp_event[i] = -1;
 		writeq_relaxed(0, dtm->base + CMN_DTM_WPn_MASK(i));