(In reply to comment #5)
> (In reply to comment #4)
> > 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:
> 
> When you disable the GPU the hardware is physically powered off so you are
> accessing non-existent registers.  You need to power up the GPU using
> vgaswitcheroo before loading/resuming the driver or access the config space
> with lspci.

I guess what I was trying to say was, does having the device in this state
before you start suspend make the power management subsystem confused?  Will it
try to "restore" the pci configuration space to 0xff?  

The radeon GPU is definitely turned on by the firmware on resume and the
apple-gmux driver turns it off if that was the state of the system when suspend
was started.

I tried a quick hack to call the "ON" function for vga-switcheroo from the
apple-gmux driver suspend hook.  But that didn't work.  However, if I do it
manually (i.e. echo ON > /sys/kernel/debug/vgaswitcheroo/switch) before
suspend, then it does seem to fix it.