I have an Ubuntu 20.04 running on a Dell Precision, to which I have connected two Samsung monitors S27H850QFU connected through a HDMI to USB-C converter. It's not exactly a HDMI to USB-C converter since has 3 inputs (HDMI, USB-C and USB 3.0) and one output (USB-C) which I connect to the laptop.
Just to clarify, I have two of these 'hubs/converters' connected to two of my laptop's USB-C ports.
The problem is that sometime, when I boot, I find a combination of the following problems with the monitors:
- One of them doesn't come up.
- One of them doesn't show all the resolutions that should be available. For instance, I see 1920x1080 as the maximum resolution while the maximum is 2560x1440.
- Sometimes I just turn off one of the monitors, but I still have the problem above.
- Sometimes the problem gets fixed by unplugging/plugging one or both monitors. Sometimes it doesn't.
- Sometimes I have one monitor plugged and working fine and, when connecting the second one, one or more of the above problems happen.
Generally, I need to reboot one or more times until the above gets fixed (that is, I have (at least) one monitor with the maximum resolution available)
I'm using the Intel Corporation UHD Graphics driver:
00:02.0 VGA compatible controller: Intel Corporation UHD Graphics (rev 05)
Subsystem: Dell Device 097e
Kernel driver in use: i915
I have listed the available resolutions when the problem is happening:
> xrandr
Screen 0: minimum 8 x 8, current 1680 x 1050, maximum 32767 x 32767
eDP-1-1 connected (normal left inverted right x axis y axis)
1920x1200 59.95 + 59.88 47.96
1920x1080 60.01 59.97 59.96 59.93
1600x1200 60.00
1680x1050 59.95 59.88
1600x1024 60.17
1400x1050 59.98
1600x900 59.99 59.94 59.95 59.82
[...]
DP-1-1 connected primary 1680x1050+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
1920x1080 60.00 50.00 59.94
1680x1050 59.88*
1600x900 60.00
1280x1024 75.02 60.02
1440x900 59.90
1280x800 59.91
1152x864 75.00
1280x720 60.00 59.94
1024x768 75.03 70.07 60.00
832x624 74.55
800x600 72.19 75.00 60.32 56.25
720x576 50.00
720x480 60.00 59.94
640x480 75.00 72.81 66.67 60.00 59.94
720x400 70.08
DP-1-2 connected (normal left inverted right x axis y axis)
2560x1440 59.95 +
1920x1080 60.00 50.00 59.94
1680x1050 59.88
1600x900 60.00
1280x1024 75.02 60.02
1440x900 59.90
1280x800 59.91
1152x864 75.00
1280x720 60.00 59.94
1024x768 75.03 70.07 60.00
832x624 74.55
800x600 72.19 75.00 60.32 56.25
720x576 50.00
720x480 60.00 59.94
640x480 75.00 72.81 66.67 60.00 59.94
720x400 70.08
DP-1-3 disconnected (normal left inverted right x axis y axis)
DP-1-1 and DP-1-2 are the monitos, Screen 0 is the laptop one. I don't know what DP-1-3 is.
I have tried as well to set the resolutions through the terminal:
1 #!/bin/bash
2 # script name: monitors.sh
3 xrandr --output DP-1-1 --mode 2560x1440 --right-of DP-1-2
4 xrandr --output DP-1-2 --mode 2560x1440 --left-of DP-1-1
and, when executing it, I get:
bash ./monitors.sh
xrandr: cannot find mode 2560x1440
I have observed that, after trying to plug in the second monitor and having the error, and recovering by unplugging it, I see 'ghost' devices in xrandr:
Screen 0: minimum 8 x 8, current 2560 x 1440, maximum 32767 x 32767
eDP-1-1 connected (normal left inverted right x axis y axis)
[...]
DP-1-1
[...]
DP-1-2 disconnected (normal left inverted right x axis y axis)
DP-1-3 disconnected (normal left inverted right x axis y axis)
I have tried to remove DP-1-2 and DP-1-3 to see if that is the problem, but neither xrandr --rmmode nor xrandr --delmode can do it.
