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Subject[PATCH] drm/sched: Extend the documentation.
Date
These comments answer all the questions I had for myself when
implementing a driver using the GPU scheduler.

Signed-off-by: Eric Anholt <eric@anholt.net>
---
include/drm/gpu_scheduler.h | 46 +++++++++++++++++++++++++++++++++----
1 file changed, 42 insertions(+), 4 deletions(-)

diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index dfd54fb94e10..c053a32341bf 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -43,10 +43,12 @@ enum drm_sched_priority {
};

/**
- * A scheduler entity is a wrapper around a job queue or a group
- * of other entities. Entities take turns emitting jobs from their
- * job queues to corresponding hardware ring based on scheduling
- * policy.
+ * drm_sched_entity - A wrapper around a job queue (typically attached
+ * to the DRM file_priv).
+ *
+ * Entities will emit jobs in order to their corresponding hardware
+ * ring, and the scheduler will alternate between entities based on
+ * scheduling policy.
*/
struct drm_sched_entity {
struct list_head list;
@@ -78,7 +80,18 @@ struct drm_sched_rq {

struct drm_sched_fence {
struct dma_fence scheduled;
+
+ /* This fence is what will be signaled by the scheduler when
+ * the job is completed.
+ *
+ * When setting up an out fence for the job, you should use
+ * this, since it's available immediately upon
+ * drm_sched_job_init(), and the fence returned by the driver
+ * from run_job() won't be created until the dependencies have
+ * resolved.
+ */
struct dma_fence finished;
+
struct dma_fence_cb cb;
struct dma_fence *parent;
struct drm_gpu_scheduler *sched;
@@ -88,6 +101,13 @@ struct drm_sched_fence {

struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);

+/**
+ * drm_sched_job - A job to be run by an entity.
+ *
+ * A job is created by the driver using drm_sched_job_init(), and
+ * should call drm_sched_entity_push_job() once it wants the scheduler
+ * to schedule the job.
+ */
struct drm_sched_job {
struct spsc_node queue_node;
struct drm_gpu_scheduler *sched;
@@ -112,10 +132,28 @@ static inline bool drm_sched_invalidate_job(struct drm_sched_job *s_job,
* these functions should be implemented in driver side
*/
struct drm_sched_backend_ops {
+ /* Called when the scheduler is considering scheduling this
+ * job next, to get another struct dma_fence for this job to
+ * block on. Once it returns NULL, run_job() may be called.
+ */
struct dma_fence *(*dependency)(struct drm_sched_job *sched_job,
struct drm_sched_entity *s_entity);
+
+ /* 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.
+ */
struct dma_fence *(*run_job)(struct drm_sched_job *sched_job);
+
+ /* Called when a job has taken too long to execute, to trigger
+ * GPU recovery.
+ */
void (*timedout_job)(struct drm_sched_job *sched_job);
+
+ /* Called once the job's finished fence has been signaled and
+ * it's time to clean it up.
+ */
void (*free_job)(struct drm_sched_job *sched_job);
};

--
2.17.0
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