Date:   Tue, 07 Aug 2018 01:12:46 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Hans Yang <hansy@...dia.com>,
        Guennadi Liakhovetski <g.liakhovetski@....de>,
        mchehab@...nel.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH resend] [media] uvcvideo: zero seq number when disabling stream

Hi Hans,

(CC'ing the linux-usb mailing list)

On Thursday, 19 October 2017 15:03:34 EEST Laurent Pinchart wrote:
> On Thursday, 19 October 2017 10:23:06 EEST Hans Yang wrote:
> > On 2017年10月18日 16:52, Guennadi Liakhovetski wrote:
> >> On Mon, 16 Oct 2017, Laurent Pinchart wrote:
> >>> 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.

Do your USB analyser traces show whether Windows sends a SET_INTERFACE(0) 
request when stopping the stream for bulk-based devices ?

> According to the USB 3.0 specification, section 9.4.5 ("Get Status"),
> 
> "Regardless of whether an endpoint has the Halt feature set, a
> ClearFeature(ENDPOINT_HALT) request always results in the data sequence
> being reinitialized to zero, and if Streams are enabled, the Stream State
> Machine shall be reinitialized to the Disabled state."
> 
> If Linux doesn't reset the sequence number when issuing a
> CLEAR_FEATURE(HALT), isn't it a Linux USB stack bug that should be fixed in
> the USB core ?

Do you have any update on whether you would consider this to be a Linux USB 
stack issue or a uvcvideo driver issue ?

> >>> 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).
> > 
> >>>> 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@...dia.com>
> >>>> ---
> >>>> 
> >>>>   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

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