I have Lenovo Thinkpad T530, with docking station. Then I have a monitor (Lenovo ThinkVision Pro2840m), and I have Displayport cable from docking station to the display.
Monitor does have speakers, and I have verified they work under Windows 7.
Under Ubuntu Mate, they are not detected: Preferences -> Hardware -> Sound only shows the internal stereo output of the laptop (which also works), and also
aplay -l only shows that. This question seems to be related, but there the device is detected automatically. I suspect this has something to do with the dock.
I am using NVIDIA binary driver 346.59 for display, under plain up-to-date Ubuntu Mate 15.04, current kernel version 3.19.0-25-generic.
How do I get the DisplayPort sound to work? Or how do I investigate the issue?