From 1b0f84380b10ee97f7d2dd191294de9017e94d1d Mon Sep 17 00:00:00 2001
From: Ben Skeggs <bskeggs@redhat.com>
Date: Thu, 11 May 2017 17:19:48 +1000
Subject: [PATCH] drm/nouveau/tmr: handle races with hw when updating the next
alarm time
If the time to the next alarm is short enough, we could race with HW and
end up with an ~4 second delay until it triggers.
Fix this by checking again after we update HW.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org
---
.../gpu/drm/nouveau/nvkm/subdev/timer/base.c | 26 ++++++++++++-------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
index 07dc82bfe3460..4e696627fdcdf 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
@@ -36,23 +36,29 @@ nvkm_timer_alarm_trigger(struct nvkm_timer *tmr)
unsigned long flags;
LIST_HEAD(exec);
- /* move any due alarms off the pending list */
+ /* Process pending alarms. */
spin_lock_irqsave(&tmr->lock, flags);
list_for_each_entry_safe(alarm, atemp, &tmr->alarms, head) {
- if (alarm->timestamp <= nvkm_timer_read(tmr))
- list_move_tail(&alarm->head, &exec);
+ /* Have we hit the earliest alarm that hasn't gone off? */
+ if (alarm->timestamp > nvkm_timer_read(tmr)) {
+ /* Schedule it. If we didn't race, we're done. */
+ tmr->func->alarm_init(tmr, alarm->timestamp);
+ if (alarm->timestamp > nvkm_timer_read(tmr))
+ break;
+ }
+
+ /* Move to completed list. We'll drop the lock before
+ * executing the callback so it can reschedule itself.
+ */
+ list_move_tail(&alarm->head, &exec);
}
- /* reschedule interrupt for next alarm time */
- if (!list_empty(&tmr->alarms)) {
- alarm = list_first_entry(&tmr->alarms, typeof(*alarm), head);
- tmr->func->alarm_init(tmr, alarm->timestamp);
- } else {
+ /* Shut down interrupt if no more pending alarms. */
+ if (list_empty(&tmr->alarms))
tmr->func->alarm_fini(tmr);
- }
spin_unlock_irqrestore(&tmr->lock, flags);
- /* execute any pending alarm handlers */
+ /* Execute completed callbacks. */
list_for_each_entry_safe(alarm, atemp, &exec, head) {
list_del_init(&alarm->head);
alarm->func(alarm);
--
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