drm/sched: Fix entities with 0 rqs.

Some blocks in amdgpu can have 0 rqs.

Job creation already fails with -ENOENT when entity->rq is NULL,
so jobs cannot be pushed. Without a rq there is no scheduler to
pop jobs, and rq selection already does the right thing with a
list of length 0.

So the operations we need to fix are:
  - Creation, do not set rq to rq_list[0] if the list can have length 0.
  - Do not flush any jobs when there is no rq.
  - On entity destruction handle the rq = NULL case.
  - on set_priority, do not try to change the rq if it is NULL.
Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/scheduler/sched_entity.c

@@ -52,12 +52,12 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
 {
 	int i;
 
-	if (!(entity && rq_list && num_rq_list > 0 && rq_list[0]))
+	if (!(entity && rq_list && (num_rq_list == 0 || rq_list[0])))
 		return -EINVAL;
 
 	memset(entity, 0, sizeof(struct drm_sched_entity));
 	INIT_LIST_HEAD(&entity->list);
-	entity->rq = rq_list[0];
+	entity->rq = NULL;
 	entity->guilty = guilty;
 	entity->num_rq_list = num_rq_list;
 	entity->rq_list = kcalloc(num_rq_list, sizeof(struct drm_sched_rq *),
@@ -67,6 +67,10 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
 
 	for (i = 0; i < num_rq_list; ++i)
 		entity->rq_list[i] = rq_list[i];
+
+	if (num_rq_list)
+		entity->rq = rq_list[0];
+
 	entity->last_scheduled = NULL;
 
 	spin_lock_init(&entity->rq_lock);
@@ -165,6 +169,9 @@ long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
 	struct task_struct *last_user;
 	long ret = timeout;
 
+	if (!entity->rq)
+		return 0;
+
 	sched = entity->rq->sched;
 	/**
 	 * The client will not queue more IBs during this fini, consume existing
@@ -264,20 +271,24 @@ static void drm_sched_entity_kill_jobs(struct drm_sched_entity *entity)
  */
 void drm_sched_entity_fini(struct drm_sched_entity *entity)
 {
-	struct drm_gpu_scheduler *sched;
+	struct drm_gpu_scheduler *sched = NULL;
 
+	if (entity->rq) {
 		sched = entity->rq->sched;
 		drm_sched_rq_remove_entity(entity->rq, entity);
+	}
 
 	/* Consumption of existing IBs wasn't completed. Forcefully
 	 * remove them here.
 	 */
 	if (spsc_queue_peek(&entity->job_queue)) {
+		if (sched) {
 			/* Park the kernel for a moment to make sure it isn't processing
 			 * our enity.
 			 */
 			kthread_park(sched->thread);
 			kthread_unpark(sched->thread);
+		}
 		if (entity->dependency) {
 			dma_fence_remove_callback(entity->dependency,
 						  &entity->cb);
@@ -362,9 +373,11 @@ void drm_sched_entity_set_priority(struct drm_sched_entity *entity,
 	for (i = 0; i < entity->num_rq_list; ++i)
 		drm_sched_entity_set_rq_priority(&entity->rq_list[i], priority);
 
+	if (entity->rq) {
 		drm_sched_rq_remove_entity(entity->rq, entity);
 		drm_sched_entity_set_rq_priority(&entity->rq, priority);
 		drm_sched_rq_add_entity(entity->rq, entity);
+	}
 
 	spin_unlock(&entity->rq_lock);
 }