Thanks for the link ! Very nice wiki.
It almost worked in my case.. almost.
coreboot boots : OK
seabios payload launch wth external GPU : OK
GRUB2 launch : Fail
-> "prefix error variable not set"
I think this has something to do with the modules..
I will try to build a clean GRUB2 with the tips provided by your link.
I gave up yesterday xD
If you're using onboard graphics, you could try to build GRUB with coreboot
build system. For me it worked fine.
Once you selected your board, rom chip size, etc.. you go in "Payload" and
select GRUB as payload.
You put "grub.cfg" in the coreboot folder and tick "use grub config" (or
similar), it will build the rom with GRUB and grub.cfg embedded into CBFS. If
you're using external GPU, that's a different story though..
IIRC, you have to use Seabios (let's call it SeaGrub) so that the external
GPU can be initialized, then you can switch to GRUB payload..
If you build a rom with GRUB only and use external GPU, screen remains black.
This config : http://imgur.com/a/ZVhnt works with onboard graphics and GRUB.