Hi Guennadi,
Thank you for the patch, and sorry for the late reply.
On Tuesday 02 September 2014 08:16:28 Guennadi Liakhovetski wrote:
> From: Aviv Greenberg <aviv.d.greenberg@xxxxxxxxx>
>
> 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.
Speaking of bulk devices, based on your experience, how do devices detect a
stream stop condition in practice ?
> Signed-off-by: Aviv Greenberg <aviv.d.greenberg@xxxxxxxxx>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx>
Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
I've taken the patch in my tree and will send a pull request for v3.20.
> ---
> drivers/media/usb/uvc/uvc_video.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c
> b/drivers/media/usb/uvc/uvc_video.c index 3394c34..c111de2 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1709,15 +1709,15 @@ 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) {
> uvc_queue_enable(&stream->queue, 0);
> return ret;
> }
>
> - if (!uvc_queue_streaming(&stream->queue))
> - return 0;
> -
> ret = uvc_init_video(stream, GFP_NOIO);
> if (ret < 0)
> uvc_queue_enable(&stream->queue, 0);
--
Regards,
Laurent Pinchart
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