drm/sched: warn about drm_sched_job_init()'s partial init

drm_sched_job_init()'s name suggests that after the function succeeded,
parameter "job" will be fully initialized. This is not the case; some
members are only later set, notably drm_sched_job.sched by
drm_sched_job_arm().

Document that drm_sched_job_init() does not set all struct members.

Document the lifetime of drm_sched_job.sched.

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241023141530.113370-2-pstanner@redhat.com

drivers/gpu/drm/scheduler/sched_main.c

@@ -771,6 +771,10 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
  * Drivers must make sure drm_sched_job_cleanup() if this function returns
  * successfully, even when @job is aborted before drm_sched_job_arm() is called.
  *
+ * Note that this function does not assign a valid value to each struct member
+ * of struct drm_sched_job. Take a look at that struct's documentation to see
+ * who sets which struct member with what lifetime.
+ *
  * WARNING: amdgpu abuses &drm_sched.ready to signal when the hardware
  * has died, which can mean that there's no valid runqueue for a @entity.
  * This function returns -ENOENT in this case (which probably should be -EIO as

include/drm/gpu_scheduler.h

@@ -340,6 +340,14 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);
 struct drm_sched_job {
 	struct spsc_node		queue_node;
 	struct list_head		list;
+
+	/**
+	 * @sched:
+	 *
+	 * The scheduler this job is or will be scheduled on. Gets set by
+	 * drm_sched_job_arm(). Valid until drm_sched_backend_ops.free_job()
+	 * has finished.
+	 */
 	struct drm_gpu_scheduler	*sched;
 	struct drm_sched_fence		*s_fence;