[PATCH 2/5] video: Allow deferring and retrying driver-specific video sync

[Alper Nebi Yasak]

The sandbox SDL driver has some code in the video uclass to rate limit
video syncs by postponing them, and forcing a sync nonetheless with a
"force" argument.

Add infrastructure for doing this through driver ops, where the driver
can request to defer a sync with -EAGAIN, and the uclass can force it by
calling the op again it until it does something.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak at gmail.com>
---
Alternatively, add "force" argument into the driver ops->video_sync().
But I think it should go away instead. The problem is video_sync() being
called irregularly and too frequently, maybe we can call it only from
cyclic at the hardware refresh rate?

 drivers/video/video-uclass.c | 2 ++
 include/video.h              | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/video-uclass.c b/drivers/video/video-uclass.c
index 7cec6362570f..accf486509cb 100644
--- a/drivers/video/video-uclass.c
+++ b/drivers/video/video-uclass.c
@@ -446,6 +446,8 @@ int video_sync(struct udevice *vid, bool force)
 
 	if (ops && ops->video_sync) {
 		ret = ops->video_sync(vid);
+		while (force && ret == -EAGAIN)
+			ret = ops->video_sync(vid);
 		if (ret)
 			return ret;
 	}
diff --git a/include/video.h b/include/video.h
index 42e57b44188d..5c4327d4e455 100644
--- a/include/video.h
+++ b/include/video.h
@@ -137,7 +137,8 @@ struct video_priv {
  *		displays needs synchronization when data in an FB is available.
  *		For these devices implement video_sync hook to call a sync
  *		function. vid is pointer to video device udevice. Function
- *		should return 0 on success video_sync and error code otherwise
+ *		should return 0 on success video_sync, -EAGAIN if it was
+ *		deferred and should be tried again, and error code otherwise
  */
 struct video_ops {
 	int (*video_sync)(struct udevice *vid);
-- 
2.40.1