Each folder contains a .dtb file, which is the compiled device tree itself, plus a .dts with the original source and a .gpio file showing the GPIO pin mappings.

Generic

The generic device tree I will use in my project, suitable for many occasions

Has 2x UART (plus the console uart), 2x I2C. 1xSPI
12 unassigned GPIO pins

Serial

Four UART interfaces and Four I2C interfaces

Has 4x UART (plus the console uart), 4x I2C
UART3 has RTC/CTS pins available too
10 unassigned GPIO pins

SPI

SPI plus Serial interfaces

Has 3x UART (plus the console uart), 3x I2C. 1xSPI
8 unassigned GPIO pins

SunXI

Vanilla, unpopulated, upstream

Has the console uart, nothing more
26 unassigned GPIO pins!

AllWinner Nezha

DO NOT USE

Included for completeness, this is the default device tree you get with the Ubuntu image.
Has the console uart, 1x I2C. 1xSPI
15 unassigned GPIO pins, 3 pre-assigned to pinctl

Examining the current DTB pin mappings:

In the tools folder there is a python script called list-pins.py.

To run it you need to be in that directory, then run python3 list-pins.py MangoPi-MQ-Pro to see a map of the current pin assignments (the same map I use in .gpio files in the folders above.)

Install and use

Installing is simple, clone this repo on to the MQ pro and, as root, copy the desired .dtb file to the /boot/dbts folder.

Then make a soft link in the root of the /boot folder named dtb-mqpro that points to the file you just copied.

Finally, edit the /boot/grub/grub.cfg file to use the new DTB for the default 'Ubuntu' target.

Reboot!

After rebooting you can re-run list-pins.py from above to verify the new mappings.

If you have errors rebooting (maybe a corrupt file if you rebuilt it etc..) you need to either boot using a USB serial adapter on the console pins and select the recover image (or edit the command and revert to the generic .dtb). Or remove the SD card, mount the /boot partition and edit the grub/grub.cfg file there.

Making Permanent:

(As Root) Edit: /etc/grub.d/10_linux line 458 to say:

  for i in "dtb-mqpro" "dtb-${version}" "dtb-${alt_version}" "dtb"; do

Note that we are adding dtb-mqpro to the start of this list, this is the 'search list' for the DTB files, the full section reads:

  dtb=
  for i in "dtb-mqpro" "dtb-${version}" "dtb-${alt_version}" "dtb"; do
    if test -e "${dirname}/${i}" ; then
      dtb="$i"
      break
    fi
  done