DM8168 VPSS_FVID2: create handle is NULL

运行saLoopBackFbdev程序，运行到ioctl(capt.fd, VIDIOC_STREAMON, &a);系统调用，就出现下面这个问题，请问是什么原因造成？

VPSS_FVID2: create handle is NULL
ti81xxvin ti81xxvin: ti81xxvin_vps_create failed
ti81xxvin ti81xxvin: Vps create failed