[PATCH v3 4/7] arm_pmu: Tidy up clear_event_idx call backs

[Suzuki K Poulose <suzuki.poulose@arm.com>]

The armpmu uses get_event_idx callback to allocate an event
counter for a given event, which marks the selected counter
as "used". Now, when we delete the counter, the arm_pmu goes
ahead and clears the "used" bit and then invokes the "clear_event_idx"
call back, which kind of splits the job between the core code
and the backend. Tidy this up by relying on the clear_event_idx
to do the book keeping, if available. Otherwise, let the core
driver do the default "clear" bit operation. This will be useful
for adding the chained event support, where we leave the event
idx maintenance to the backend.

Also, when an event is removed from the PMU, reset the hw.idx
to indicate that a counter is not allocated for this event,
to help the backends do better checks. This will be also used
for the chain counter support.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
Changes since v2:
 - Reset the event counter after an event is removed.
---
 arch/arm/kernel/perf_event_v7.c |  2 ++
 drivers/perf/arm_pmu.c          | 17 +++++++++++++----
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
index fd7ce01..765d265 100644
--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -1637,6 +1637,7 @@ static void krait_pmu_clear_event_idx(struct pmu_hw_events *cpuc,
 	bool venum_event = EVENT_VENUM(hwc->config_base);
 	bool krait_event = EVENT_CPU(hwc->config_base);
 
+	clear_bit(hwc->idx, cpuc->used_mask);
 	if (venum_event || krait_event) {
 		bit = krait_event_to_bit(event, region, group);
 		clear_bit(bit, cpuc->used_mask);
@@ -1966,6 +1967,7 @@ static void scorpion_pmu_clear_event_idx(struct pmu_hw_events *cpuc,
 	bool venum_event = EVENT_VENUM(hwc->config_base);
 	bool scorpion_event = EVENT_CPU(hwc->config_base);
 
+	clear_bit(hwc->idx, cpuc->used_mask);
 	if (venum_event || scorpion_event) {
 		bit = scorpion_event_to_bit(event, region, group);
 		clear_bit(bit, cpuc->used_mask);
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index e3766a8..6e10e8c 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -227,6 +227,16 @@ static void armpmu_start(struct perf_event *event, int flags)
 	armpmu->enable(event);
 }
 
+static void armpmu_clear_event_idx(struct arm_pmu *armpmu,
+				   struct pmu_hw_events *hw_events,
+				   struct perf_event *event)
+{
+	if (armpmu->clear_event_idx)
+		armpmu->clear_event_idx(hw_events, event);
+	else
+		clear_bit(event->hw.idx, hw_events->used_mask);
+}
+
 static void
 armpmu_del(struct perf_event *event, int flags)
 {
@@ -237,11 +247,10 @@ armpmu_del(struct perf_event *event, int flags)
 
 	armpmu_stop(event, PERF_EF_UPDATE);
 	hw_events->events[idx] = NULL;
-	clear_bit(idx, hw_events->used_mask);
-	if (armpmu->clear_event_idx)
-		armpmu->clear_event_idx(hw_events, event);
-
+	armpmu_clear_event_idx(armpmu, hw_events, event);
 	perf_event_update_userpage(event);
+	/* Clear the allocated counter */
+	hwc->idx = -1;
 }
 
 static int
-- 
2.7.4