Arch Linux

ashic

Member

Registered: 2020-01-22

Posts: 68

[solved] 5K Dell UP2715K display over Thunderbolt 3?

I've got a Dell Precision 5510 connected to a Dell UP2715K display over Thunderbolt 3 via a Plugable Thunderbolt 3 to Dual DisplayPort Output Display Adapter for Thunderbolt 3 Windows Systems. I've been running the monitor in 4k all this time. However, on Windows, it runs in 5K. The xrandr output is

DP-1 connected 3840x2160+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
   3840x2160     60.00*+  60.00  
   2560x1440     59.95 +
   2560x2880     59.98    29.99  
   1920x1200     59.88  
   1920x1080     60.00  
   1600x1200     60.00  
   1680x1050     59.95  
   1280x1024     60.02  
   1280x800      59.81  
   1024x768      60.00  
   800x600       60.32  
   640x480       60.00    59.94  
DP-2 connected (normal left inverted right x axis y axis)
   848x480       59.74 +
   2560x2880     59.98    29.99  

5K is 5120x2880. 5120=2560*2. So it appears that the monitor is showing up as two tiles when arranged next to each other horizontally, results in 5K. Which makes sense as the monitor uses two dvi inputs. I can see both panels are displayed as expected. I'm wondering how I can make then work as one screen.

I'm using Arch (antergos distro, latest kernel) with i3wm.

Last edited by ashic (2020-12-17 21:33:20)

ashic

Member

Registered: 2020-01-22

Posts: 68

Re: [solved] 5K Dell UP2715K display over Thunderbolt 3?

Ah... and just after posting, I've managed to figure it out. It needed xrandr 1.5.1, which I didn't have last time I tried this. Here are the steps:

1. "xrandr --output DP-2 --left-of DP-1 auto" . Running this puts the content of DP-1 to the right of DP-2, and DP-2 looks a bit wonky. Previously this induced flicker and I'd stop trying. Seems to work with the latest kernel.
2. "xrandr --listmonitors" now shows eDP-1, DP-1, and DP-2. eDP-1 is the laptop LCD. Previously, this command showed only DP-1 as DP-2 wasn't being used.
3. "xrandr --setmonitor Dell auto DP-1,DP-2" . auto atuomatically detects screen size, etc. And combines the panels into one. i3wm got a bit confused but a reload of i3 sorted out the issue.

So years after having my setup and my 5K monitor, I now finally have 5K in linux. Working great. Probably need to play with magnification ratios a bit. And HD videos look crapper. But all in all, working well.