* [PATCH] UVC: Remove extra commit on resume()
@ 2014-09-02 6:16 Guennadi Liakhovetski
2015-01-02 11:35 ` Laurent Pinchart
0 siblings, 1 reply; 2+ messages in thread
From: Guennadi Liakhovetski @ 2014-09-02 6:16 UTC (permalink / raw)
To: Linux Media Mailing List; +Cc: Laurent Pinchart
From: Aviv Greenberg <aviv.d.greenberg@intel.com>
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>
---
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);
--
1.7.9.5
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] UVC: Remove extra commit on resume()
2014-09-02 6:16 [PATCH] UVC: Remove extra commit on resume() Guennadi Liakhovetski
@ 2015-01-02 11:35 ` Laurent Pinchart
0 siblings, 0 replies; 2+ messages in thread
From: Laurent Pinchart @ 2015-01-02 11:35 UTC (permalink / raw)
To: Guennadi Liakhovetski; +Cc: Linux Media Mailing List
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@intel.com>
>
> 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@intel.com>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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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2015-01-02 11:35 ` Laurent Pinchart
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