credits to: HejinYo for sharing the initial steps that can be found here.
I just made some updates, and added step to compile kernel for the displays
It should be able to support most of the available display drivers in the kernel. (Check the kernel directory for the available source)
We just need to modify compile and update into Radxa Zero.
# install dtc
sudo apt-get install device-tree-compiler
# optional / useful to test display
# framebuffer imageviewer
sudo apt-get install fbi# navigate to device tree path
# depends on your kernel version
cd /boot/dtbs/5.10.xx-x-amlogic-xxxxxxxxxxxxx/amlogic/overlay
# create new device tree file and
# copy the contents of meson-g12a-spi-lcd.dts
# then configure pin assignment
sudo nano meson-g12a-spi-lcd.dts
# pin assignment, check values for A and B
<pin> = <0x2b A B>
# to get value of A, for example your pin is 36
# goto https://wiki.radxa.com/Zero/hardware/gpio
# get the ping number (Function 1 pin),
# ex. pin 36 -> GPIOH_8, then
# goto https://github.com/radxa/kernel/blob/linux-5.10.y-radxa-zero/include/dt-bindings/gpio/meson-g12a-gpio.h
# get the equivalent pin defined, for GPIOH_8, its 8, set it for A
# to get value of B, if it is initialized as HIGH, set to 1
# if initialized as LOW, set to 0
# save the dts file and compile to dtbo
# there may be some warnings, but its fine
sudo dtc -@ -I dts -O dtb -o meson-g12a-spi-lcd.dtbo meson-g12a-spi-lcd.dts
# update /boot/uEnv.txt
# add the new overlay to the overlays
# add the params
overlays=meson-g12a-spi-lcd
param_spidev_spi_bus=1
param_spidev_max_freq=10000000
# Compile the kernel, go to kernel-linux-5.10.y-radxa-zero/drivers/staging/fbtft/ directory
# if your display is st7789, you should take that .ko file
# be sure to change xxxx's to your own path
make && sudo cp {fb_st7789v.ko,fbtft.ko} /usr/lib/modules/5.10.xx-x-amlogic-xxxxxxxxxxxxx/kernel/drivers/staging/fbtft/
# lastly, reboot
sudo reboot now
# Connect the pins accordingly
# To verify the kernel is running
dmesg | grep fbtft
# to test display, get a sample image
sudo fbi -d /dev/fb1 -T 1 -noverbose -a <sample_image>