Dell U2415 connected to K620 via DP1.2 MST is blank. Driver 384.111 on Ubuntu 16.04.
I have spent many many hours trying to get daisy-chaining working across three Dell UltraSharp U2415 monitors I have.
In the first instance I am only trying to succeed with a mere two monitors. Troubleshooting appears to have been complicated by various overlapping shortcomings in the products, linux and/or DP standard but I have managed to minify these to get something which feels like it should almost be working.
Shortcoming 1: The monitors ship with DP1.1a enabled by default in the settings menu but DP1.2 required for MST. According to Dell, NVIDIA drivers do not like it when the last monitor in the chain has DP1.2 enabled. Mitigation: I have made sure only the intermediary monitor has DP1.2 enabled and that the end-of-chain monitor has DP1.2 disabled.
Shortcoming 2: When one of these Dell monitors has no visuals to display it enters ‘energy saving mode’. When this happens it appears that the driver perceives this as a change in monitor configuaration. When the OS adjusts for this perceived change in configuration the monitor wakes from energy saving mode, the driver reverts back to the previous configuration and a loop condition is created. Mitigation: I have configured the monitors OSD settings menu to its maximum timeout setting (60s), the screen will not enter energy saving mode so long as this menu is open. I can navigate the menu to reset the timeout timer thus can prevent the loop condition.
So what is the current state?
I have all three moniors connected as follows:
- Monitor A: Connected to K620 DP out. Operating in DP1.2 mode.
- Monitor B: Connected to Monitor A DP out. Operating in DP1.1a mode but blank.
- Monitor C: Connected to K620 DVI out. Operating on HDMI input.
In NVIDIA X Server settings all three displays are detected and their layout matches their physica layout on my desk:
Rough steps to reproduce:
- Install Ubuntu 16.04 desktop.
- Update apt.
- Install any upgrades.
- Install HWE stack.
- sudo ubuntu-drivers autoinstall
- configure hardware as above
nvidia-bug-report.log.gz (160 KB)