drm/panfrost: Prevent concurrent resets

If a job times out in slot 0 while a reset is performed because a job
timed out in slot 1, the drm-sched core can get into a deadlock.
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190418084305.45021-1-tomeu.vizoso@collabora.com

drivers/gpu/drm/panfrost/panfrost_device.c

@@ -98,6 +98,7 @@ int panfrost_device_init(struct panfrost_device *pfdev)
 	struct resource *res;
 
 	mutex_init(&pfdev->sched_lock);
+	mutex_init(&pfdev->reset_lock);
 	INIT_LIST_HEAD(&pfdev->scheduled_jobs);
 
 	spin_lock_init(&pfdev->hwaccess_lock);

drivers/gpu/drm/panfrost/panfrost_device.h

@@ -78,6 +78,7 @@ struct panfrost_device {
 	struct list_head scheduled_jobs;
 
 	struct mutex sched_lock;
+	struct mutex reset_lock;
 
 	struct {
 		struct devfreq *devfreq;

drivers/gpu/drm/panfrost/panfrost_job.c

@@ -384,6 +384,8 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
 		job_read(pfdev, JS_TAIL_LO(js)),
 		sched_job);
 
+	mutex_lock(&pfdev->reset_lock);
+
 	for (i = 0; i < NUM_JOB_SLOTS; i++)
 		drm_sched_stop(&pfdev->js->queue[i].sched);
 
@@ -406,6 +408,8 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
 	/* restart scheduler after GPU is usable again */
 	for (i = 0; i < NUM_JOB_SLOTS; i++)
 		drm_sched_start(&pfdev->js->queue[i].sched, true);
+
+	mutex_unlock(&pfdev->reset_lock);
 }
 
 static const struct drm_sched_backend_ops panfrost_sched_ops = {