[RFC PATCH 04/10] drm/sched: Add generic scheduler message interface

[Matthew Brost <matthew.brost@intel.com>]

Add generic schedule message interface which sends messages to backend
from the drm_gpu_scheduler main submission thread. The idea is some of
these messages modify some state in drm_sched_entity which is also
modified during submission. By scheduling these messages and submission
in the same thread their is not race changing states in
drm_sched_entity.

This interface will be used in XE, new Intel GPU driver, to cleanup,
suspend, resume, and change scheduling properties of a drm_sched_entity.

The interface is designed to be generic and extendable with only the
backend understanding the messages.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/scheduler/sched_main.c | 58 +++++++++++++++++++++++++-
 include/drm/gpu_scheduler.h            | 29 ++++++++++++-
 2 files changed, 84 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 2795021efe7b..9dc3378e9c5e 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -1055,6 +1055,54 @@ drm_sched_pick_best(struct drm_gpu_scheduler **sched_list,
 }
 EXPORT_SYMBOL(drm_sched_pick_best);
 
+/**
+ * drm_sched_add_msg - add scheduler message
+ *
+ * @sched: scheduler instance
+ * @msg: message to be added
+ *
+ * Can and will pass an jobs waiting on dependencies or in a runnable queue.
+ * Messages processing will stop if schedule run wq is stopped and resume when
+ * run wq is started.
+ */
+void drm_sched_add_msg(struct drm_gpu_scheduler *sched,
+		       struct drm_sched_msg *msg)
+{
+	spin_lock(&sched->job_list_lock);
+	list_add_tail(&msg->link, &sched->msgs);
+	spin_unlock(&sched->job_list_lock);
+
+	/*
+	 * Same as above in drm_sched_run_wq_queue, try to kick worker if
+	 * paused, harmless if this races
+	 */
+	if (!sched->pause_run_wq)
+		queue_work(sched->run_wq, &sched->work_run);
+}
+EXPORT_SYMBOL(drm_sched_add_msg);
+
+/**
+ * drm_sched_get_msg - get scheduler message
+ *
+ * @sched: scheduler instance
+ *
+ * Returns NULL or message
+ */
+static struct drm_sched_msg *
+drm_sched_get_msg(struct drm_gpu_scheduler *sched)
+{
+	struct drm_sched_msg *msg;
+
+	spin_lock(&sched->job_list_lock);
+	msg = list_first_entry_or_null(&sched->msgs,
+				       struct drm_sched_msg, link);
+	if (msg)
+		list_del(&msg->link);
+	spin_unlock(&sched->job_list_lock);
+
+	return msg;
+}
+
 /**
  * drm_sched_main - main scheduler thread
  *
@@ -1068,6 +1116,7 @@ static void drm_sched_main(struct work_struct *w)
 
 	while (!READ_ONCE(sched->pause_run_wq)) {
 		struct drm_sched_entity *entity;
+		struct drm_sched_msg *msg;
 		struct drm_sched_fence *s_fence;
 		struct drm_sched_job *sched_job;
 		struct dma_fence *fence;
@@ -1075,12 +1124,16 @@ static void drm_sched_main(struct work_struct *w)
 
 		cleanup_job = drm_sched_get_cleanup_job(sched);
 		entity = drm_sched_select_entity(sched);
+		msg = drm_sched_get_msg(sched);
 
 		if (cleanup_job)
 			sched->ops->free_job(cleanup_job);
 
+		if (msg)
+			sched->ops->process_msg(msg);
+
 		if (!entity) {
-			if (!cleanup_job)
+			if (!cleanup_job && !msg)
 				break;
 			continue;
 		}
@@ -1089,7 +1142,7 @@ static void drm_sched_main(struct work_struct *w)
 
 		if (!sched_job) {
 			complete_all(&entity->entity_idle);
-			if (!cleanup_job)
+			if (!cleanup_job && !msg)
 				break;
 			continue;
 		}
@@ -1181,6 +1234,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
 
 	init_waitqueue_head(&sched->job_scheduled);
 	INIT_LIST_HEAD(&sched->pending_list);
+	INIT_LIST_HEAD(&sched->msgs);
 	spin_lock_init(&sched->job_list_lock);
 	atomic_set(&sched->hw_rq_count, 0);
 	INIT_DELAYED_WORK(&sched->work_tdr, drm_sched_job_timedout);
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index 3e421f5a710c..18172ae63ab7 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -398,6 +398,23 @@ enum drm_gpu_sched_stat {
 	DRM_GPU_SCHED_STAT_ENODEV,
 };
 
+/**
+ * struct drm_sched_msg - an in-band (relative to GPU scheduler run queue)
+ * message
+ *
+ * Generic enough for backend defined messages, backend can expand if needed.
+ */
+struct drm_sched_msg {
+	/** @link: list link into the gpu scheduler list of messages */
+	struct list_head		link;
+	/**
+	 * @private_data: opaque pointer to message private data (backend defined)
+	 */
+	void				*private_data;
+	/** @opcode: opcode of message (backend defined) */
+	unsigned int			opcode;
+};
+
 /**
  * struct drm_sched_backend_ops - Define the backend operations
  *	called by the scheduler
@@ -475,6 +492,12 @@ struct drm_sched_backend_ops {
          * and it's time to clean it up.
 	 */
 	void (*free_job)(struct drm_sched_job *sched_job);
+
+	/**
+	 * @process_msg: Process a message. Allowed to block, it is this
+	 * function's responsibility to free message if dynamically allocated.
+	 */
+	void (*process_msg)(struct drm_sched_msg *msg);
 };
 
 /**
@@ -486,6 +509,7 @@ struct drm_sched_backend_ops {
  * @timeout: the time after which a job is removed from the scheduler.
  * @name: name of the ring for which this scheduler is being used.
  * @sched_rq: priority wise array of run queues.
+ * @msgs: list of messages to be processed in @work_run
  * @job_scheduled: once @drm_sched_entity_do_release is called the scheduler
  *                 waits on this wait queue until all the scheduled jobs are
  *                 finished.
@@ -493,7 +517,7 @@ struct drm_sched_backend_ops {
  * @job_id_count: used to assign unique id to the each job.
  * @run_wq: workqueue used to queue @work_run
  * @timeout_wq: workqueue used to queue @work_tdr
- * @work_run: schedules jobs and cleans up entities
+ * @work_run: schedules jobs, cleans up jobs, and processes messages
  * @work_tdr: schedules a delayed call to @drm_sched_job_timedout after the
  *            timeout interval is over.
  * @pending_list: the list of jobs which are currently in the job queue.
@@ -517,6 +541,7 @@ struct drm_gpu_scheduler {
 	long				timeout;
 	const char			*name;
 	struct drm_sched_rq		sched_rq[DRM_SCHED_PRIORITY_COUNT];
+	struct list_head		msgs;
 	wait_queue_head_t		job_scheduled;
 	atomic_t			hw_rq_count;
 	atomic64_t			job_id_count;
@@ -570,6 +595,8 @@ void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
 
 void drm_sched_job_cleanup(struct drm_sched_job *job);
 void drm_sched_wakeup(struct drm_gpu_scheduler *sched);
+void drm_sched_add_msg(struct drm_gpu_scheduler *sched,
+		       struct drm_sched_msg *msg);
 void drm_sched_run_wq_stop(struct drm_gpu_scheduler *sched);
 void drm_sched_run_wq_start(struct drm_gpu_scheduler *sched);
 void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad);
-- 
2.34.1