[PATCH v7 1/3] drm/sched: Adjust outdated docu for run_job()

Philipp Stanner
2025-03-05T13:06:05Z

The documentation for drm_sched_backend_ops.run_job() mentions a certain
function called drm_sched_job_recovery(). This function does not exist.
What's actually meant is drm_sched_resubmit_jobs(), which is by now also
deprecated.

Furthermore, the scheduler expects to "inherit" a reference on the fence
from the run_job() callback. This, so far, is also not documented.

Remove the mention of the removed function.

Discourage the behavior of drm_sched_backend_ops.run_job() being called
multiple times for the same job.

Document the necessity of incrementing the refcount in run_job().

Signed-off-by: Philipp Stanner <phasta@kernel.org>
---
include/drm/gpu_scheduler.h | 34 ++++++++++++++++++++++++++++++----
1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index 50928a7ae98e..6381baae8024 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -410,10 +410,36 @@ struct drm_sched_backend_ops {
struct drm_sched_entity *s_entity);

/**
- * @run_job: Called to execute the job once all of the dependencies
- * have been resolved. This may be called multiple times, if
- * timedout_job() has happened and drm_sched_job_recovery()
- * decides to try it again.
+ * @run_job: Called to execute the job once all of the dependencies
+ * have been resolved.
+ *
+ * @sched_job: the job to run
+ *
+ * The deprecated drm_sched_resubmit_jobs() (called by &struct
+ * drm_sched_backend_ops.timedout_job) can invoke this again with the
+ * same parameters. Using this is discouraged because it violates
+ * dma_fence rules, notably dma_fence_init() has to be called on
+ * already initialized fences for a second time. Moreover, this is
+ * dangerous because attempts to allocate memory might deadlock with
+ * memory management code waiting for the reset to complete.
+ *
+ * TODO: Document what drivers should do / use instead.
+ *
+ * This method is called in a workqueue context - either from the
+ * submit_wq the driver passed through drm_sched_init(), or, if the
+ * driver passed NULL, a separate, ordered workqueue the scheduler
+ * allocated.
+ *
+ * Note that the scheduler expects to 'inherit' its own reference to
+ * this fence from the callback. It does not invoke an extra
+ * dma_fence_get() on it. Consequently, this callback must take a
+ * reference for the scheduler, and additional ones for the driver's
+ * respective needs.
+ *
+ * Return:
+ * * On success: dma_fence the driver must signal once the hardware has
+ * completed the job ("hardware fence").
+ * * On failure: NULL or an ERR_PTR.
*/
struct dma_fence *(*run_job)(struct drm_sched_job *sched_job);

--
2.48.1