Displayport MST and the Linux driver


I have a two-monitor setup; the monitors are a Dell U2415 and Dell U2412M. I want to drive them via Displayport daisy-chain (MST). My video card is a recent NVIDIA GTX 1660 Super.

The setup I have is full-size Displayport cable from the video card to the Dell U2415 (where DP1.2 is enabled) and then a second full-size Displayport cable from the U2415 DP-out to the U2412M (which does not support DP1.2, but I thought that was OK for the final monitor in the chain).

Under Windows 10, with the NVIDIA Geforce driver, this arrangement works perfectly and has been stable for some time so I believe the hardware is all working OK and correctly configured.

However with the NVIDIA Geforce Linux driver (currently version 440.64) the arrangement does not work. During boot, the screens are mirrored. After starting the X server, the U2412M goes into soft-off (powersave) mode (and can’t be woken) while the U2415 alternates between “on” and a black screen every 2-3 seconds. There do not seem to any errors messages in the log files to diagnose what is happening; my config. files just contain default entries.

If I drive the two monitors separately via 2 displayport outputs then all is well. But the MST arrangement would be very convenient to be able to connect other devices to share both screens so I would like to get it working if possible.

I’ve tried the standard suggestion posted on forums several years ago of running “xset dpms force off” and then moving the mouse to reset - this does not change the behaviour.

Do you have any suggestions of what I could try to get this working?


To my experience, DP daisy-chaining is unreliable/broken with the linux driver, even if it runs on start, it’ll break once a monitor goes into standby.