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 :-) > > > 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.sha...@st.com> -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
