Device is Orange Pi4

For example, so that it displays:

* Mounting debug filesystem ...
 [ ok ]
 * Mounting config filesystem ...
 [ ok ]
 * Mounting cgroup filesystem ...
 [ ok ]
 * Remounting devtmpfs on /dev ...
 [ ok ]
 * Mounting /dev/mqueue ...
 [ ok ]
 * Mounting /dev/shm ...
 [ ok ]
 * Creating list of required static device nodes for the current kernel ...
 [ ok ]
 * Starting udev ...
 [ ok ]
 * Generating a rule to create a /dev/root symlink ...
 [ ok ]
 * Populating /dev with existing devices through uevents ...

Kernel is 5.4.23-rockchip64

Edit /boot/boot.cmd. Comment out strings about the console and insert one pointing yo ttyS2.

#if test "${console}" = "display" || test "${console}" = "both"; then setenv consoleargs "console=tty1"; fi
#if test "${console}" = "serial" || test "${console}" = "both"; then setenv consoleargs "console=ttyS2,1500000 ${consoleargs}"; fi
setenv consoleargs "console=ttyS2,1500000 ${consoleargs}"

Then:

# Recompile with:
# mkimage -C none -A arm -T script -d /boot/boot.cmd /boot/boot.scr

Reboot.