Zaxter's post in Opening serial port causes kernal panic was marked as the answer
I was able to solve the problem. It was related to UART settings in the Fex file.
Somehow, I hadn't set the pull-up on UART6 & UART7. ->
[uart_para6]
uart_used = 1
uart_port = 6
uart_type = 2
uart_tx = port:PI12<3><default><default><default>
uart_rx = port:PI13<3><default><default><default>
# ^
# |
# Here
It should've been ->
[uart_para6]
uart_used = 1
uart_port = 6
uart_type = 2
uart_tx = port:PI12<3><1><default><default>
uart_rx = port:PI13<3><1><default><default>
I guess I will be moving to the mainline kernel in the future.
Zaxter's post in Opening serial port causes kernal panic was marked as the answer