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.
Signed-off-by: Aviv Greenberg <aviv.d.greenberg@xxxxxxxxx>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx>
---
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
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