I've tried two different DisplayPort to mDP cables - MacBook Pro Retina does not see the Dell U3014. Rebooted, tried everything. Lastest OS with all updates. Anyone else get the Dell U3014 working with a MacBook Pro Retina?
I too am having the same problem. I get a message saying that there is no DisplayPort cable connected. It works with the DisplayPort to Dual Link DVI adapter.
I bought a mDP DP cable that was listed as specifically being DP 1.2 compatible. I spent 30 minutes on the phone with Apple Support resetting the system board, booting in safe mode, etc. It still doesn't work. I tried a 2011 13" MBP and it didn't work either. I used a mDP to DP cable to connect the rMBP to a 24" HP display and it worked.
I bought a mini DisplayPort to mini DisplayPort cable and it works. Also, in browsing the web I realized that the U3014 has a DP output. I believe I was plugging the DP cable into that port instead of the input port. Kind of stupid. I didn't know the monitor had a DP output port. I haven't tried the DP input port yet, but would be surprised if it doesn't work.
However, with the computer plugged into the mDP port, the text is very blocky. I noticed that the monitor is not in RGB mode. Instead it is in YPbPr (or probably YCbCr) mode. Changing to RGB makes the colors funny. However, I found this
I ran the ruby script that was posted in the thread in the above link. It created a directory with a file in it. I copied the directory to /System/Library/Displays/Overrides, as indicated. I rebooted and all seems well.
Have you made sure you are using the DP input instead of the DP output? See below for details.