Created attachment 73542 [details] [review]
Add quirk to efifb for iMac 12,1

Here's a patch to try. But after some more poking around I'm wondering why this
is needed. The kernel seems to get the information about the GOP framebuffer
for most recent Macs without quirking, so it makes me wonder why it doesn't
work on this machine.

Just to check one obvious point, are you either running with the stock Ubuntu
kernels or else with CONFIG_FB_EFI=y? An easy way to verify this is to boot the
machine and run 'grep CONFIG_FB_EFI /boot/config-$(uname -r)'. This should
output 'CONFIG_FB_EFI=y' if your kernel is configured to include the EFI
framebuffer support.