Seth Forshee on Tuesday published his latest work in this area for Apple display switching support to the kernel mailing list. The patches build upon vga_switcheroo to support display switching with the GMUX. While these three patches allow for display switching, graphics drivers may still have issues with this support on Apple hardware due to missing/invalid vBIOS information on Apple computers. The patches at least fix a GMUX state restoration issue that some MacBook users have seen.
This series adds display switching support for Apple laptops. The first two patches contain preparatory changes to vga_switcheroo, and the third contains the changes to support display switching with the gmux.Matthew Garrett has also been working on Apple GMUX support for the newer Apple Intel/NVIDIA graphics hardware per these patches from this week. Matthew Garrett's been playing around with an Apple Retina MacBook Pro and trying to better the Linux support, but from my testing thus far, I absolutely cannot recommend running any Linux distribution at this time bare-metal on Apple's newest notebook with its incredible display. There's many outstanding problems and all of the issues will likely not be all ironed out and found in tier-one distributions until early next year at least.
While these patches will allow switching the display mux, most Macbook owners will not be able to switch GPUs in practice until the graphics drivers are updated to deal with missing or incorrect vbios information on Apple machines. These patches do fix an issue seen by some users of Linux on Macbooks, however. These users will switch to the internal GPU in OS X and then reboot into Linux to save power, but after S3 the gmux gets reset to the discrete GPU. Adding the display mux support will fix this problem by restoring the gmux state during resume.