So I have my new Dell P2715Q connected to a Thunderbolt port on my MacBook Pro Retina 15" Mid-2015 using the supplied DisplayPort cable, in SST mode.
When I plugged it in the first time, it worked perfectly at 4K@60. But: when the MacBook goes to sleep, the display does not wake when the laptop does.
Once woken, the MacBook is aware there is a second monitor attached (I can move the mouse off the edge of the MacBook monitor), but the Dell shows black.
Going into Display Preferences and hitting "Detect Displays" fixes everything back to how it should be, but it's a huge pain that it doesn't do it automatically. When I do this, the MacBook monitor does not dip to black (like it usually does when I plug in a monitor), but the Dell wakes. Makes me think that the MacBook has opened the display stream but is forgetting to send anything to it.
Anyone have any ideas?