drm/sched: Document what the timedout_job method should do

The documentation is a bit vague and doesn't really describe what the
->timedout_job() is expected to do. Let's add a few more details.

v5:
* New patch

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210630062751.2832545-2-boris.brezillon@collabora.com

diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index d18af49..aa90ed1 100644 (file)
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -239,6 +239,20 @@ struct drm_sched_backend_ops {
         * @timedout_job: Called when a job has taken too long to execute,
         * to trigger GPU recovery.
         *
+        * This method is called in a workqueue context.
+        *
+        * Drivers typically issue a reset to recover from GPU hangs, and this
+        * procedure usually follows the following workflow:
+        *
+        * 1. Stop the scheduler using drm_sched_stop(). This will park the
+        *    scheduler thread and cancel the timeout work, guaranteeing that
+        *    nothing is queued while we reset the hardware queue
+        * 2. Try to gracefully stop non-faulty jobs (optional)
+        * 3. Issue a GPU reset (driver-specific)
+        * 4. Re-submit jobs using drm_sched_resubmit_jobs()
+        * 5. Restart the scheduler using drm_sched_start(). At that point, new
+        *    jobs can be queued, and the scheduler thread is unblocked
+        *
         * Return DRM_GPU_SCHED_STAT_NOMINAL, when all is normal,
         * and the underlying driver has started or completed recovery.
         *