Hi @JerryChang,
Thanks for your thorough explanation. I usually include my custom .dtsi into .../hardware/nvidia/platform/t18x/lanai/kernel-dts/tegra186-p3636-0001-p3509-0000-a01.dts
during the driver development.
I will apply the modification that you shared in TX2 NX RS232 Communication Problem - #14 by JerryChang and if it works, I will put this ticket in Resolved. Otherwise, I might have further questions.
Thanks,
K.