edk2-platforms VS edk2-platforms

Almost certainly the former as the latter is barely usable (if not outright unusable). Ampere says the Altra and Altra Max are compliant with Arm SBSA and SBBR, so compliant OSes that support UEFI and ACPI should just work (no need for SoC-specific kernel trees/etc like you tend to find on SBCs with lower-end SoCs). The devkit product page also mentions that it uses "open source EDKII" firmware. It looks like Ampere released the source code for their EDK II port and is working on upstreaming it. They also published a guide on how to build the firmware.

There's an rpi3/4 edk2 uefi firmware you'd have to use in order to run it, but it does exist

It's not entirely open source (it still depends on the FSP binaries), but Intel has released UEFI initialization code for older platforms. They also contribute platform support to coreboot (though this also depends on the FSP).

If you prefer building it yourself: https://github.com/tianocore/edk2-platforms/tree/master/Platform/RaspberryPi/RPi4

> They prefer to keep inner workings secret

https://github.com/tianocore/edk2-platforms/tree/master/Sili...

Almost certainly the former as the latter is barely usable (if not outright unusable). Ampere says the Altra and Altra Max are compliant with Arm SBSA and SBBR, so compliant OSes that support UEFI and ACPI should just work (no need for SoC-specific kernel trees/etc like you tend to find on SBCs with lower-end SoCs). The devkit product page also mentions that it uses "open source EDKII" firmware. It looks like Ampere released the source code for their EDK II port and is working on upstreaming it. They also published a guide on how to build the firmware.