Setup
I have an nVidia GeForce GTX 1080 with two daisy chained (MST) Dell U2715H monitors under Ubuntu 16.04.
The hardware and the OS has the DisplayPort 1.2 support and the drivers work properly.
Problem
I turned on DisplayPort 1.2 for both monitors and they show up in the settings and in the nVidia control panel, I can even move my mouse to the second screen (so the desktop is extended too). The monitor plugged to the PC works perfectly fine, but the daisy chained monitor (the one plugged into the other monitor) is somewhy stays in sleep mode so I have a black screen. Why? How can I fix this?
Best Answer
tl;dr
Run the followind command on startup, and the problem will be virtually
hackedsolved:Cause of the problem
After some search I found this forum post and it turned out that everything works properly except that the monitor is stuck in sleep mode. If you wait for the system to sleep (or force it) when it wakes, everything will go back to normal.
According to the user replies, it seems like that this problem is common when you use Dell monitors with an nVidia graphics card.
Solution
As fabbari pointed out, you can force the monitors to sleep with the command
xset dpms force off, so you just need to move the mouse and everything is back to normal. This is still more of a workaround, but if you search for "startup" in the dash and add a new startup application, you can paste the command so it will automatically run on startup. This happens so seamlessly, that you doesn't even notice it, so I consider it a perfect solution.