[RFC v1 6/9] drm/xe/hw_engine_group: Ensure safe transition between execution modes

[Francois Dugast]

Provide a way to safely transition execution modes of the hw engine
group ahead of the actual execution. When necessary, either wait for
running jobs to complete or preempt them, thus ensuring mutual
exclusion between modes EXEC_MODE_LR and EXEC_MODE_DMA_FENCE.

Unlike a mutex, the rw_semaphore used in this context allows multiple
submissions in the same mode.

Signed-off-by: Francois Dugast <francois.dugast at intel.com>
---
 drivers/gpu/drm/xe/xe_hw_engine.c | 67 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/xe/xe_hw_engine.h |  3 ++
 2 files changed, 70 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_hw_engine.c b/drivers/gpu/drm/xe/xe_hw_engine.c
index dc75dfe6187a..4f539711357a 100644
--- a/drivers/gpu/drm/xe/xe_hw_engine.c
+++ b/drivers/gpu/drm/xe/xe_hw_engine.c
@@ -1278,3 +1278,70 @@ static int xe_hw_engine_group_wait_for_dma_fence_jobs(struct xe_hw_engine_group
 
 	return 0;
 }
+
+static int switch_mode(struct xe_hw_engine_group *group,
+		       enum xe_hw_engine_group_execution_mode new_mode)
+{
+	int err = 0;
+
+	lockdep_assert_held(&group->mode_sem);
+
+	if (group->cur_mode == new_mode)
+		return 0;
+	else if (group->cur_mode == EXEC_MODE_LR && new_mode == EXEC_MODE_DMA_FENCE)
+		err = xe_hw_engine_group_suspend_lr_jobs(group);
+	else if (group->cur_mode == EXEC_MODE_DMA_FENCE && new_mode == EXEC_MODE_LR)
+		err = xe_hw_engine_group_wait_for_dma_fence_jobs(group);
+	else
+		err = -EINVAL;
+
+	if (err)
+		return err;
+
+	group->cur_mode = new_mode;
+
+	return 0;
+}
+
+/**
+ * xe_hw_engine_group_get_mode() - Get the group to execute in the new mode
+ * @group: The hw engine group
+ * @mode: The new execution mode
+ *
+ * Return: 0 if successful, -EINTR if locking failed.
+ */
+int xe_hw_engine_group_get_mode(struct xe_hw_engine_group *group,
+				enum xe_hw_engine_group_execution_mode mode)
+{
+	int err = down_read_interruptible(&group->mode_sem);
+
+	if (err)
+		return err;
+
+	if (mode != group->cur_mode) {
+		up_read(&group->mode_sem);
+		err = down_write_killable(&group->mode_sem);
+		if (err)
+			return err;
+
+		if (mode != group->cur_mode) {
+			err = switch_mode(group, mode);
+			if (err) {
+				up_write(&group->mode_sem);
+				return err;
+			}
+		}
+		downgrade_write(&group->mode_sem);
+	}
+
+	return err;
+}
+
+/**
+ * xe_hw_engine_group_put() - Put the group
+ * @group: The hw engine group
+ */
+void xe_hw_engine_group_put(struct xe_hw_engine_group *group)
+{
+	up_read(&group->mode_sem);
+}
diff --git a/drivers/gpu/drm/xe/xe_hw_engine.h b/drivers/gpu/drm/xe/xe_hw_engine.h
index ce59d83a75ad..fce0adf6a7c4 100644
--- a/drivers/gpu/drm/xe/xe_hw_engine.h
+++ b/drivers/gpu/drm/xe/xe_hw_engine.h
@@ -73,5 +73,8 @@ u64 xe_hw_engine_read_timestamp(struct xe_hw_engine *hwe);
 
 int xe_hw_engine_group_add_exec_queue(struct xe_hw_engine_group *group, struct xe_exec_queue *q);
 int xe_hw_engine_group_del_exec_queue(struct xe_hw_engine_group *group, struct xe_exec_queue *q);
+int xe_hw_engine_group_get_mode(struct xe_hw_engine_group *group,
+				enum xe_hw_engine_group_execution_mode mode);
+void xe_hw_engine_group_put(struct xe_hw_engine_group *group);
 
 #endif
-- 
2.43.0