Okay, thanks.

I suspect at least part of the problem may be related to efifb. I don't see
that it's being used on your machine, and I note that it has a bunch of quirks
for making it work with various Mac hardware. If we add a quirk for your
machine efifb should then be able to identify the radeon as the default vga
device and use it for the console framebuffer. I'm guessing this won't fix the
problem with the 32-bit builds, but it should at least remove the need for
i915.disable=1 with the 64-bit build.

To make a patch I'll need some DMI information for your machine. Could you send
me the output from the following commands?

 dmidecode -s bios-vendor
 dmidecode -s system-product-name