[media] uvcvideo: Remove extra commit on resume()

The UVC spec is a bit vague wrt devices using bulk endpoints,
specifically, how to signal to a device to start streaming.

For devices using isoc endpoints, the sequence for start streaming is:
1) The host sends PROBE_CONTROL(SET_CUR) PROBE_CONTROL(GET_CUR)
2) Host selects desired config and calls COMMIT_CONTROL(SET_CUR)
3) Host selects an alt interface other then zero - e.g SELECT_ALTERNATE_INTERFACE(1)
4) The device starts streaming

However for devices using bulk endpoints, there must be *no* alt interface
other than setting zero. From the UVC spec:
"A VideoStreaming interface containing a bulk endpoint for streaming shall
support only alternate setting zero. Additional alternate settings containing
bulk endpoints are not permitted in a device that is compliant with the Video
Class specification."

So for devices using bulk endpoints, step #3 above is irrelevant, and thus
cannot be used as an indication for the device to start streaming.
So in practice, such devices start streaming immediately after a
COMMIT_CONTROL(SET_CUR).

In the uvc resume() handler, an unsolicited commit is sent, which causes
devices using bulk endpoints to start streaming unintentionally.

This patch modifies resume() handler to send a commit only if streaming
needs to be reestablished, i.e if the device was actually streaming before is
was suspended.

Signed-off-by: Aviv Greenberg <aviv.d.greenberg@intel.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 9637e8b..20ccc9d 100644 (file)
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1734,13 +1734,13 @@ int uvc_video_resume(struct uvc_streaming *stream, int reset)
 
        uvc_video_clock_reset(stream);
 
+       if (!uvc_queue_streaming(&stream->queue))
+               return 0;
+
        ret = uvc_commit_video(stream, &stream->ctrl);
        if (ret < 0)
                return ret;
 
-       if (!uvc_queue_streaming(&stream->queue))
-               return 0;
-
        return uvc_init_video(stream, GFP_NOIO);
 }