To change your current console loglevel to debug
echo 8 > /proc/sys/kernel/printk
First, you can enable v4l2 core debug logs. Check what driver is associated with which device file:
ls /dev/video/by-name/ -l
lrwxrwxrwx 1 root root 12 Jan 1 03:00 coda -> ../../video2
lrwxrwxrwx 1 root root 12 Jan 1 03:00 imx-ipuv3-scale -> ../../video0
lrwxrwxrwx 1 root root 12 Jan 1 03:00 vout -> ../../video1
So, enable debug logging for coda by writing to the corresponding video2 file in /sys:
echo 3 > /sys/class/video4linux/video2/debug
More details: https://www.kernel.org/doc/Documentation/video4linux/v4l2-framework.txt
If the tested driver uses the v4l2_mem2mem framework you can get M2M logs with:
echo Y > /sys/module/v4l2_mem2mem/parameters/debug
Get also internal vb2 logs with:
echo 3 > /sys/module/videobuf2_core/parameters/debug
And optionally more logs using the dynamic debug feature: (https://www.kernel.org/doc/Documentation/dynamic-debug-howto.txt). Example:
echo "module my_driver +p" > /sys/kernel/debug/dynamic_debug/control