Hi Bhupesh, On Tuesday 24 April 2012 02:46:22 Bhupesh SHARMA wrote: > On Monday, April 23, 2012 7:47 PM Laurent Pinchart wrote: > > On Monday 23 April 2012 02:24:53 Bhupesh SHARMA wrote: > > > Hi Laurent, > > > > > > I have been doing some experimentation with the UVC webcam gadget along > > > with the UVC user-space application which you have written. > > > > > > The UVC webcam gadget works fine with the user space application > > > handling the CONTROL events and providing DATA events. Now, I wish to > > > interface a real v4l2 device, for e.g. VIVI or more particularly a > > > soc_camera based host and subdev pair. > > > > > > Now, I see that I can achieve this by opening the UVC and V4L2 devices > > > and doing MMAP -> REQBUF -> QBUF -> DQBUF calls on both the devices per > > > the UVC control event received. But this will involve copying the video > > > buffer in the user-space application from v4l2 (_CAPTURE) to uvc > > > (_OUTPUT) domains, which will significantly reduce the video capture > > > performance. > > > > > > Is there a better solution to this issue? Maybe doing something like a > > > RNDIS gadget does with the help of u_ether.c like helper routines. But > > > if I remember well it also requires the BRCTL (Bridge Control Utility) > > > in userspace to route data arriving on usb0 to eth0 and vice-versa. Not > > > sure though, if it does copying of a skb buffer from ethernet to usb > > > domain and vice-versa. > > > > To avoid copying data between the two devices you should use USERPTR > > instead of MMAP on at least one of the two V4L2 devices. The UVC gadget > > driver doesn't support USERPTR yet though. This shouldn't be too difficult > > to fix, we need toreplace the custom buffers queue implementation with > > videobuf2, as has been done in the uvcvideo driver. > > I was thinking of using the USERPTR method too, but I realized that > currently neither UVC webcam gadget nor soc-camera subsystem supports this > IO method. They support only MMAP IO as of now :( Both soc-camera and the UVC gadget driver should be ported to videobuf2 to fix the problem. > > I'll try to implement this. Would you then be able to test patches ? > > For sure, I can test your patches on my setup. I had a quick look, but there's a bit more work than expected. The UVC gadget driver locking scheme needs to be revisited. I unfortunately won't have time to work on that in the next couple of weeks, and very probably not before end of June. Sorry. If you want to give it a try, I can provide you with some pointers. > BTW, I was exploring GSTREAMER to use the data arriving from soc-camera > (v4l2) capture device '/dev/video1' via 'v4l2src' plugin and routing the > same to the UVC gadget '/dev/video0' via the 'v4l2sink' plugin. > > Don't know if this can work cleanly in my setup and whether GSTREAMER > actually performs a buffer copy internally. But I will at-least give it a > try :) There will definitely be a buffer copy (and actually two copies, as the UVC gadget driver performs a second copy internally) if you don't use USERPTR. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
