1. modify the file kernel\arch\arm64\boot\dts\rockchip\rk3399-linux.dtsi
chosen {
bootargs = "earlycon=uart8250,mmio32,0xff1a0000 console=ttyFIQ0 rw root=PARTUUID=614e0000-0000 rootfstype=ext4 rootwait coherent_pool=1m";
};
2. recompile kernel
3. reflash kernel to the board.
It is recommended to back up the original rk3399-linux.dtsi before modification.