As the title states, it seems that with the upgrade to Windows 10, the ability to use Multi-Stream (MST) through Displayport (1.2) ceased to function. This is definitely not a hardware issue as it works on another system and worked on this one prior to the upgrade.
Here's the Details:
Current Configuration is Precision M3800 (Intel 4600 / Quadro K1100m) and 2 Dell U3014 30" Monitors. Laptop was purchased about a week or two ago with 16GB RAM and 500GB SSD All Running Windows 8.1
The M3800 is connected by mDisplayPort to the DisplayPort in on Monitor 1. This monitor has DP1.2 enabled for Daisy Chaining Screens. The DP output on Monitor 1 is connected to the DP input on Monitor 2.
Before the upgrade to windows 10, The above setup was working perfectly, and I had 3 screens that I could move windows around on.(Built-in LCD + the 2 30") After the upgrade, Neither of the two Monitors display anything (Built-in works fine at UHD and HD Res). Device manager shows both 30" screens attached and when I unplug the mDP cable from my laptop, both screens disappear from Device Manager. (Plug in, they reappear) "Display Settings" in Windows only shows 1 screen (the Built-in LCD on the laptop) and not the two monitors but Device manager lists them with no errors.
Latest drivers for both the Intel and Nvidia cards downloaded from Dell with no luck. (even tried the ones from Intel & Nvidia (again no luck)
If I turn off DP1.2 on Monitor 1 (the primary that the 2nd connects to), the Two monitors mirror each other and can be used to mirror my Laptop LCD or as a 2nd display (however useless 2 30" Screens are that have the same info... at least they light up). Re-Enable DP 1.2 on the Primary Screen and both screens go black and disappear from Display settings (Still in Device Manager however)
Testing these screens on my HP Desktop (Windows 7 with an Nvidia Quadro K4000 Card) shows that they still work fine in DP1.2 Daisy Chained (MST) mode coming from one single DP output (Which Is what I expected since It worked fine before with Windows 8.1 on my laptop)
Summary - Windows 7, & Windows 8.1 works just fine with DP 1.2 enabled. Not on Windows.
What are my next steps?
Also curious if you resolved this - I recently updated to Windows 10 and have run into the same problem with my M3800 and two Dell U2415 monitors.
Update: after spending about an hour on the phone with ProSupport, I've been told the only option is to roll back to 8.1 and/or wait for driver updates to resolve this problem.
I Confirm that the issue is fixed with the latest Windows update for Win 10 (X64) Both of my 30" screens are being driven by the one Thunderbolt connection. It even works through my Elgato Thunderbolt dock which makes it even better. One connection for everything (Except Power)
Hmm. Interesting. That is very strange, because my monitors were working fine after upgrading to windows 10 over a month ago. Just today Nov 10 they stopped working. My problem is exactly as described within the original post. Using Del U2414H, and laptop is a Dell XPS13. DP 1.2 does not work at all anymore which *** because I hate windows 8.1. Windows 10 was initially a breath of fresh air, but now this. They seem to be moving backwards now.