1) The kernel is V4L2 enabled, e.g.,
CONFIG_VIDEO_DEV=y
CONFIG_VIDEO_V4L2_COMMON=y
CONFIG_VIDEO_MEDIA=y
CONFIG_USB_VIDEO_CLASS=y
CONFIG_V4L_USB_DRIVERS=y
CONFIG_USB_VIDEO_CLASS_INPUT_EVDEV=y

2) The permission of /dev/video0 is set 0666 in /ueventd.xxxx.rc