Failing to boot with both APU and PCIe graphics enabled

[Nobu]

I'm running ArchLinux (testing repo disabled) with latest updates, and the system boots fine with either the APU or PCIe graphics enabled, but when I enable both at once and boot, the system freezes (screen blank) and slowly (not as fast as if in BIOS, but faster than when idle) heats up.

System Specs:

AMD A10-6800K APU
Radeon HD7770 (VisionTek)
Gigabyte GA-F2A88XN-WIFI Motherboard (uEFI)
1 x 8GB DDR3 RAM

Kernel: 3.12.8-1-ARCH
Mesa: 10.0.2-1
xorg-server: 1.5.0-5

I've also tried booting both with and without DPM enabled...any ideas?

[Nobu]

Oh, there's a new minor version of xf86-video-ati and linux, and a new linux-firmware package. I'll try upgrading those and see if that helps, but still open to suggestions.

[Nobu]

Nope, still no good. Fwiw, Windows boots fine, so it's probably not a hardware issue.

[gradinaruvasile]

Check your xorg logs.

[Nobu]

Didn't think there would be any logs, looked like it failed before then. I was wrong, of course. -_-

Looks like page-flipping is failing for some reason ("device or resource busy"?), and it gets into some sort of infinite loop (which would explain why it heats up). Here's the log (too big to post here).

I'll try again with page-flip disabled and see how that goes.

[Nobu]

Nevermind, all that noise is from a previous boot, where I kept switching between my PS3 and my desktop, and it had to re-register the monitor. Not sure what the page-flip errors were from, but since that wasn't a session where I had both gpus enabled, I doubt it's relevant.

I've tried a few times since to see if I could get a log after a failed boot, but with no success. Looks like it fails too soon in the boot process after all. It is consistant, though--no issue reproducing the problem. :/