In order to get the webcam running that is identified by lsusb as

Bus 002 Device 003: ID 05a9:7670 OmniVision Technologies, Inc. OV7670 Webcam

you just have to enable quirks mode for the uvcvideo kernel module:

echo "options uvcvideo quirks=0x100" > /etc/modprobe.d/uvcvideo.conf

After that, reboot or reload the kernel module (sudo rmmod uvcvideo && sudo modprobe uvcvideo). This seems to work on most recent Linux distributions and has been tested by myself on Xubuntu 14.04. If not, check that a corresponding video device has been created. More details about that issue (which I had not), can be found in a post on marvin.im (German only)