On Tue, Apr 21, 2015 at 11:58:20AM +0200, Lukas Wunner wrote:
On MBPs, the panel is not connected to one of the gpus, but to the gmux chip (the "handler" in vga_switcheroo speak). Initially the gmux is switched to the discrete gpu. The integrated i915 gpu is therefore unable to detect the LVDS (or eDP) connector on bootup and switching to the integrated gpu will lead to a black screen. The solution is to temporarily switch the DDC lines to the integrated gpu when reading the EDID, which the gmux is capable of. Lack of support for this in vga_switcheroo is pretty much the only obstacle to get gpu switching to work on MBPs.
My testing suggested that changing the DDC lines didn't change auxch, so this approach doesn't work for eDP. Have you found otherwise?