Hi Laurent, > -----Original Message----- > From: Laurent Pinchart [mailto:laurent.pinchart@xxxxxxxxxxxxxxxx] > Sent: Monday, April 23, 2012 7:47 PM > To: Bhupesh SHARMA > Cc: linux-usb@xxxxxxxxxxxxxxx; linux-media@xxxxxxxxxxxxxxx; > balbi@xxxxxx; g.liakhovetski@xxxxxx > Subject: Re: Using UVC webcam gadget with a real v4l2 device > > Hi Bhupesh, > > 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 to > replace 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 :( > > I'll try to implement this. Would you then be able to test patches ? For sure, I can test your patches on my setup. 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 :) 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
