Dear @JerryChang ,
It seems that I found the solution for my issue in the following thread : TX2 NX RS232 Communication Problem - #14 by JerryChang
However, In the 3 steps you described, I wonder how to obtain the /Linux_for_Tegra/bootloader/t186ref/tegra186-bpmp-p3636-0001-a00-00.dtb again after disassembling it to remove the configuration related to the uartc (or serial@c280000 or ttyTHS2), please?
Thanks in advance and best regards,
K.