So I’ve tried Coreboot/TianoCore (on chip) + Grub2(EFI)/Ubuntu (on disk), and it did’t worked. I have a black screen with a blinking cursor (top left screen).

I’ve tried with Clover/macOS instead of Ubuntu, same result.

In the mean time, I’ve tried the stock UEFI Bios (on chip) + Grub2(EFI)/Ubuntu (on 1st disk, 1st to boot) + Clover(EFI)/macOS (on 2nd disk), well, Grub(EFI) can boot Clover (which boot macOS).

So I’ve tried to build a Grub2 EFI as payload for Coreboot, but without success. When building Grub2, there is the "—with-plaform=" option, and it’s either —with-plaform=coreboot or —with-plaform=efi. It doesn’t seem to be possible to select both. And of course Grub2 build —with-plaform=coreboot cannot boot Clover (nor macOS).

So for now, I’m stuck.. Maybe I’ll try Coreboot/Seabios/Duet(Tianocore)