[PATCH v3 1/4] media: uvcvideo: report AUTO_UPDATE controls as volatile

[Michael Jordan]

uvcvideo re-reads controls flagged UVC_CTRL_FLAG_AUTO_UPDATE from the
device instead of trusting its cache, as the device may change their
value on its own. That is what V4L2_CTRL_FLAG_VOLATILE describes, but
the driver does not report it to userspace.

Report V4L2_CTRL_FLAG_VOLATILE for AUTO_UPDATE controls. Writes to a
volatile control are ignored unless V4L2_CTRL_FLAG_EXECUTE_ON_WRITE is
also set, and uvcvideo sends every write to the device, so also report
EXECUTE_ON_WRITE when the control is writable.

Suggested-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
Reviewed-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
Reviewed-by: Hans de Goede <johannes.goede@xxxxxxxxxxxxxxxx>
Assisted-by: Claude:claude-fable-5
Signed-off-by: Michael Jordan <jordan.mymail@xxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_ctrl.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 3ca108b83f1d..aceb263103e9 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -1840,6 +1840,17 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
 	if ((ctrl->info.flags & UVC_CTRL_FLAG_GET_MAX) &&
 	    (ctrl->info.flags & UVC_CTRL_FLAG_GET_MIN))
 		v4l2_ctrl->flags |= V4L2_CTRL_FLAG_HAS_WHICH_MIN_MAX;
+	if (ctrl->info.flags & UVC_CTRL_FLAG_AUTO_UPDATE) {
+		v4l2_ctrl->flags |= V4L2_CTRL_FLAG_VOLATILE;
+		/*
+		 * Writes to a volatile control are documented to be ignored
+		 * unless EXECUTE_ON_WRITE is also reported. The driver sends
+		 * every write of a writable control to the device, so report
+		 * the flag accordingly.
+		 */
+		if (ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR)
+			v4l2_ctrl->flags |= V4L2_CTRL_FLAG_EXECUTE_ON_WRITE;
+	}
 
 	if (mapping->master_id)
 		__uvc_find_control(ctrl->entity, mapping->master_id,
-- 
2.43.0