Re: [PATCH resend] [media] uvcvideo: zero seq number when disabling stream

[Hans Yang]

Hi Laurent and Guennadi,

On 2017å10æ18æ 16:52, Guennadi Liakhovetski wrote:
> Hi Laurent,
>
> On Mon, 16 Oct 2017, Laurent Pinchart wrote:
>
> > Hi Hans,
> >
> > (CC'ing Guennadi Liakhovetski)
> >
> > Thank you for the patch.
> >
> > On Friday, 15 September 2017 09:27:51 EEST Hans Yang wrote:
> > > For bulk-based devices, when disabling the video stream,
> > > in addition to issue CLEAR_FEATURE(HALT), it is better to set
> > > alternate setting 0 as well or the sequnce number in host
> > > side will probably not reset to zero.
> >
> > The USB 2.0 specificatin states in the description of the SET_INTERFACE
> > request that "If a device only supports a default setting for the specified
> > interface, then a STALL may be returned in the Status stage of the request".
> >
> > The Linux implementation of usb_set_interface() deals with this by handling
> > STALL conditions and manually clearing HALT for all endpoints in the
> > interface, but I'm still concerned that this change could break existing bulk-
> > based cameras. Do you know what other operating systems do when disabling the
> > stream on bulk cameras ? According to a comment in the driver Windows calls
> > CLEAR_FEATURE(HALT), but the situation might have changed since that was
> > tested.

Sorry I did not mention that it is about SS bulk-based cameras using 
sequence number technique.
From my observations, invoking usb_clear_halt() will reset the endpoint 
in the device side via CLEAR_FEATURE(HALT)
and reset the sequence number as well; however usb_reset_endpoint() does 
not reset the host side endpoint with xhci driver,
then the sequence number will mismatch in next time stream enable.
I can always observe this through a bus analyzer on Linux implementation 
whatever X86 or ARM based.
This is not observed on the Windows.

> > Guennadi, how do your bulk-based cameras handle this ?
>
> I don't know what design decisions are implemented there, but I tested a
> couple of cameras for sending a STREAMOFF after a few captured buffers,
> sleeping for a couple of seconds, requeuing buffers, sending STREAMON and
> capturing a few more - that seems to have worked. "Seems" because I only
> used a modified version of capture-example, I haven't checked buffer
> contents.
>
> BTW, Hans, may I ask - what cameras did you use?

I have three SS bulk-based cameras as follows:
e-con Systems See3CAM_CU130 (2560:c1d0)
Leopard ZED (2b03:f580)
Intel(R) RealSense(TM) Camera SR300 (8086:0aa5)

I can observe the same issue on all above;
besides, to reproduce issue do not let the camera enter suspend because 
it will *help* to reset the sequence number through usb_set_interface(0).

> Thanks
> Guennadi
>
> > > Then in next time video stream start, the device will expect
> > > host starts packet from 0 sequence number but host actually
> > > continue the sequence number from last transaction and this
> > > causes transaction errors.
> >
> > Do you mean the DATA0/DATA1 toggle ? Why does the host continue toggling the
> > PID from the last transation ? The usb_clear_halt() function calls
> > usb_reset_endpoint() which should reset the DATA PID toggle.
> >
> > > This commit fixes this by adding set alternate setting 0 back
> > > as what isoch-based devices do.
> > >
> > > Below error message will also be eliminated for some devices:
> > > uvcvideo: Non-zero status (-71) in video completion handler.
> > >
> > > Signed-off-by: Hans Yang <hansy@xxxxxxxxxx>
> > > ---
> > >   drivers/media/usb/uvc/uvc_video.c | 5 ++---
> > >   1 file changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_video.c
> > > b/drivers/media/usb/uvc/uvc_video.c index fb86d6af398d..ad80c2a6da6a 100644
> > > --- a/drivers/media/usb/uvc/uvc_video.c
> > > +++ b/drivers/media/usb/uvc/uvc_video.c
> > > @@ -1862,10 +1862,9 @@ int uvc_video_enable(struct uvc_streaming *stream,
> > > int enable)
> > >
> > >   	if (!enable) {
> > >   		uvc_uninit_video(stream, 1);
> > > -		if (stream->intf->num_altsetting > 1) {
> > > -			usb_set_interface(stream->dev->udev,
> > > +		usb_set_interface(stream->dev->udev,
> > >   					  stream->intfnum, 0);
> > > -		} else {
> > > +		if (stream->intf->num_altsetting == 1) {
> > >   			/* UVC doesn't specify how to inform a bulk-based device
> > >   			 * when the video stream is stopped. Windows sends a
> > >   			 * CLEAR_FEATURE(HALT) request to the video streaming
> >
> > --
> > Regards,
> >
> > Laurent Pinchart

Regards,
Hans Yang
--nvpublic--