Using UVC webcam gadget with a real v4l2 device

[Bhupesh SHARMA <bhupesh.sharma@st.com>]

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.

Any idea is much appreciated.

Thanks for your help,
Bhupesh