drm/nouveau/tmr: avoid processing completed alarms when adding a new one

The idea here was to avoid having to "manually" program the HW if there's
a new earliest alarm.  This was lazy and bad, as it leads to loads of fun
races between inter-related callers (ie. therm).

Turns out, it's not so difficult after all.  Go figure ;)

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org

1 files changed, 13 insertions, 3 deletions

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
index d898787d514c..f2a86eae0a0d 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
@@ -86,12 +86,22 @@ nvkm_timer_alarm(struct nvkm_timer *tmr, u32 nsec, struct nvkm_alarm *alarm)
                         if (list->timestamp > alarm->timestamp)
                                 break;
                 }
+
                 list_add_tail(&alarm->head, &list->head);
+
+                /* Update HW if this is now the earliest alarm. */
+                list = list_first_entry(&tmr->alarms, typeof(*list), head);
+                if (list == alarm) {
+                        tmr->func->alarm_init(tmr, alarm->timestamp);
+                        /* This shouldn't happen if callers aren't stupid.
+                         *
+                         * Worst case scenario is that it'll take roughly
+                         * 4 seconds for the next alarm to trigger.
+                         */
+                        WARN_ON(alarm->timestamp <= nvkm_timer_read(tmr));
+                }
         }
         spin_unlock_irqrestore(&tmr->lock, flags);
-
-        /* process pending alarms */
-        nvkm_timer_alarm_trigger(tmr);
 }
 
 void