https://bugs.freedesktop.org/show_bug.cgi?id=26891

--- Comment #47 from Bruno bonbons67@internet.lu ---

Radeon now works for me on a MBP 8,2 booted from efistub in Linux 3.8.x. Can anyone else confirm this? You just need to make sure you add the PCI IDs to the xorg for both cards. Should Xorg detect them automatically? Is this another bug?

For nouveau on a MBA also booted via EFI stub I was told that "detection of display by Xorg" happened through some magic bit set by first going through efifb prior to native driver.

Without going through efifb Xorg didn't want to choose the available nVidia GPU. (though linux console happily used the GPU).

Possibly the same applies to radeon.