So I was messing around with my new OrangePi-5+ and installed the EDK2 UEFI firmware for Rockchip RK3588 platforms onto the SPI flash (/dev/mtdblock0). After which I tried all sorts of images and kernels with varying success, only the 5.10.160-legacy-rk3588 kernel would really have a working display. Until I tried a generic UEFI arm64 image (Jammy-CLI on a USB stick) which gave a working display, albeit at 1080p max. (my monitor is 4K) with no acceleration (after the extra steps), and installed the Mate desktop (just my preference).
The big caveat is that it does not recognize the SD-card, EMMC or SPI-flash, just regular drives (e.g. sda/nvme0n1 etc) and I'm sure a lot of other hardware isn't properly recognized either. But all of that was fixed by simply installing the old legacy kernel with apt, making a symbolic link to the correct dtb in /boot and updating grub, and a reboot later everything worked fine, the desktop popped up in 4K with acceleration and all. In the end I installed the whole thing to an NVME with armbian-config, which didn't create the separate EFI partition, so I had to corrected it manually, but that is another story.
What surprises me is that the UEFI-arm64 kernel does not seem to need a Device-Tree-Blob, in fact it doesn't even boot with its own rk3588-orangepi-5-plus.dtb.
Anyway if anyone want's to try this I'd suggest using Balena etcher to write the ED2K firmware onto an SD-card, and a generic UEFI armbian to an USB stick so you won't have to mess up anything permanently. Plug the stick in a USB2 port as it chokes during boot on the USB3 (blue) ports. And you will need a lot of patience as booting from a USB2 stick will be rather slow to say the least.
Install legacy kernel:
sudo apt update
sudo apt install linux-image-legacy-rk35xx
Create the symbolic link: (If you try this on another board or with another kernel version, you will need to adjust the link for the appropriate DTB instead)
sudo ln -s /usr/lib/linux-image-5.10.160-legacy-rk35xx/rockchip/rk3588-orangepi-5-plus.dtb /boot/dtb-5.10.160-legacy-rk35xx
Bonus tip, set the legacy kernel as a GRUB's default: (optional, adjust for different kernels)
sudo echo 'GRUB_DEFAULT="Armbian GNU/Linux, with Linux 5.10.160-legacy-rk35xx"' > /etc/default/grub.d/99-legacy.cfg
GRUB should now automatically pick up on the DTB after updating:
sudo update-grub
So far the only downside I have found is that the audio outputs are all labeled "Built-in Audio Stereo", which was easy to solve by adding some udev-rules as the Armbian build system does when building a regular OrangePi-5+ image.
