https://github.com/RAMJAC-digital/edk2-rk3588

This may be slightly out of date, but these patches allow HDMI out on uefi for the Max, and can probably be easily modified this for the Ultra. If there is interest I can look into this later on tonight and test on an Ultra. The HDMI device tree isn't too bad, you can kinda guess the address offsets, but you will need to dive into the 3588 refernece manual. There are some design flaws in these boards around using SPI for the wifi and bluetooth and haven't had these work yet. Vulkan hardware support is alright, and can run Chromium and Niri without issues. Ghostty doesn't as it is OpenGL only.

I use these baords for aarch64 linux builds and a basic desktop environment, and it's been pretty rock solid with EDK2. Take a gander ya'll.