Hi Laurent, > -----Original Message----- > From: Laurent Pinchart [mailto:laurent.pinchart@xxxxxxxxxxxxxxxx] > Sent: Saturday, July 07, 2012 6:37 PM > To: Bhupesh SHARMA > Cc: linux-usb@xxxxxxxxxxxxxxx; balbi@xxxxxx; linux- > media@xxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx > Subject: Re: [PATCH 5/5] usb: gadget/uvc: Add support for > 'USB_GADGET_DELAYED_STATUS' response for a set_intf(alt-set 1) command > > Hi Bhupesh, > > On Tuesday 03 July 2012 23:47:14 Bhupesh SHARMA wrote: > > On Wednesday, June 20, 2012 3:19 AM Laurent Pinchart wrote: > > > On Friday 01 June 2012 15:08:58 Bhupesh Sharma wrote: > > > > This patch adds the support in UVC webcam gadget design for > providing > > > > USB_GADGET_DELAYED_STATUS in response to a set_interface(alt > setting 1) > > > > command issue by the Host. > > > > > > > > The current UVC webcam gadget design generates a STREAMON event > > > > corresponding to a set_interface(alt setting 1) command from the > Host. > > > > This STREAMON event will eventually be routed to a real V4L2 > device. > > > > > > > > To start video streaming, it may be required to perform some > register > > > > writes to a camera sensor device over slow external busses like > I2C or > > > > SPI. So, it makes sense to ensure that we delay the STATUS stage > of the > > > > set_interface(alt setting 1) command. > > > > > > > > Otherwise, a lot of ISOC IN tokens sent by the Host will be > replied to > > > > by zero-length packets by the webcam device. On certain Hosts > this may > > > > even> lead to ISOC URBs been cancelled from the Host side. > > > > > > > > So, as soon as we finish doing all the "streaming" related stuff > on the > > > > real V4L2 device, we call a STREAMON ioctl on the UVC side and > from here > > > > we call the 'usb_composite_setup_continue' function to complete > the > > > > status stage of the set_interface(alt setting 1) command. > > > > > > That sounds good, thank you for coming up with a solution to this > > > issue. > > > > > > > Further, we need to ensure that we queue no video buffers on the > UVC > > > > webcam gadget, until we de-queue a video buffer from the V4L2 > device. > > > > Also, we need to enable UVC video related stuff at the first QBUF > ioctl > > > > call itself, as the application will call the STREAMON on UVC > side only > > > > when it has dequeued sufficient buffers from the V4L2 side and > queued > > > > them to the UVC gadget. So, the UVC video enable stuff cannot be > done in > > > > STREAMON ioctl call. > > > > > > Is that really required ? First of all, the userspace application > can > > > queue buffers before it calls VIDIOC_STREAMON. Assuming it doesn't, > the > > > gadget driver calls uvc_video_enable() at streamon time, which then > calls > > > uvc_video_pump(). As no buffer is queued, the function will return > without > > > queuing any USB request, so we shouldn't have any problem. > > > > I think that while working with a real video device, it will be > possible to > > queue a buffer at UVC end only when atleast one buffer has been > dequeued > > from the V4L2 device side (and has some real data). > > > > This is because for a uvc buffer being queued we need to pass the > v4l2 > > buffer's buffer.start and buffer.length in the qbuf call at UVC side. > > I agree with you, queuing a buffer on the UVC gadget side will usually > require > starting capture and waiting for a frame on a V4L2 source device. > However, > unless I'm mistaken, the UVC gadget code already deals with that > situation > correctly. As I explained, when your application calls VIDIOC_STREAMON > on the > UVC gadget, the uvc_video_pump() will not find any V4L2 buffer to be > transferred, and will return without queuing any URB. It will then be > called > again by VIDIOC_QBUF, and will then start the transfer. > > Adding support for USB_GADGET_DELAYED_STATUS is thus a good idea, but > the pre- > streaming state is in my opinion not needed. Feel free to prove me > wrong > though :-) I did some extensive tests and also managed to reproduce the problem Georgios mentioned regarding UVC not able to stream when an application using the webcam is stopped and started again (sorry Georgios, it took me some time to finish all the checks, and thanks for pointing out the issue) You are right the PRE_STREAMING state is not required. I will resend the patches 4/5 and 5/5 of this patchset with all your comments addressed in the next couple of days. > > > > For the same we add two more UVC states: > > > > - PRE_STREAMING : not even a single buffer has been queued > to UVC > > > > - BUF_QUEUED_STREAMING_OFF : one video buffer has been > queued to UVC > > > > but we have not yet enabled STREAMING on UVC > side. > > > > > > > > Signed-off-by: Bhupesh Sharma <bhupesh.sharma@xxxxxx> > > -- Regards, Bhupesh -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
