I'm not sure if this has anything to do with this bug, but the PCI config space
is all messed up when running on the integrated GPU:

# cat /sys/kernel/debug/vgaswitcheroo/switch 
0:IGD:+:Pwr:0000:00:02.0
1:DIS: :Off:0000:01:00.0
2:DIS-Audio: :Off:0000:01:00.1
# lspci -s 01:00 -xx
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Whistler [Radeon HD 6600M/6700M/7600M Series] (rev ff)
00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
10: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
20: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
30: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Turks/Whistler
HDMI Audio [Radeon HD 6000 Series] (rev ff)
00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
10: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
20: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
30: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Maybe this is why suspend/resume doesn't work?  Should the apple gmuxer remove
the radeon device from the list of pci devices when in this state?  (Like
hotplugging?)