Using rkdeveloptool

Once maskroom button is pressed on rockchip device, the device will enter into loader mode.
Then we need to loader custom firmware that enables us to internal flash of the device.

sudo rkdeveloptool ld MiniLoaderall.bin

Now we can create a copy of device flash

sudo rkdeveloptool rl 0 0xffffffff android-backup.img

Then we can start writing our new Linux OS

sudo rkdeveloptool gpt partitions.txt
sudo rkdeveloptool wlx boot uboot.img 
sudo rkdeveloptool wlx misc misc.img 
sudo rkdeveloptool wlx boot  boot.img 
sudo rkdeveloptool wlx recovery recovery.img 
sudo rkdeveloptool wlx rootfs ubuntu20-lxqt-rootfs.img 
sudo rkdeveloptool wlx oem oem.img 
sudo rkdeveloptool wlx userdata userdata.img 

The example content of partitions.txt file:

CMDLINE: mtdparts=rk29xxnand:0x00002000@0x00004000(uboot),0x00002000@0x00006000(misc),0x00020000@0x00008000(boot),0x00020000@0x00028000(recovery),0x00010000@0x00048000(backup),0x00c00000@0x00058000(rootfs),0x00040000@0x00c58000(oem),-@0x00c98000(userdata:grow)
uuid:rootfs=614e0000-0000-4b53-8000-1d28000054a9

Moderl RockChip SOC boot flow