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#1 2022-05-29 16:04:04

LinuxFan84
Member
Registered: 2021-07-12
Posts: 6

USB-C DisplayPort - Bug or normal behaviour?

Hi guys

I am not sure if this is a bug or if it is a normal behavior:

I have a Lenovo Ideapad and a docking station plugged into the USB-C slot. The docking station has two HDMI slots (and some USB and Ethernet).
I boot the laptop with the docking station connected and I have the following output with xrandr:

Screen 0: minimum 320 x 200, current 5120 x 1440, maximum 16384 x 16384
eDP connected (normal left inverted right x axis y axis)
   1920x1080     60.00 +
   1680x1050     60.00  
   1280x1024     60.00  
   1440x900      60.00  
   1280x800      60.00  
   1280x720      60.00  
   1024x768      60.00  
   800x600       60.00  
   640x480       60.00  
HDMI-A-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-1 connected primary 2560x1440+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
   2560x1440     59.95*+
   1920x1200     59.95  
   2048x1080     60.00  
   1920x1080     60.00    50.00    59.94  
   1600x1200     60.00  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
DisplayPort-2 connected 2560x1440+2560+0 (normal left inverted right x axis y axis) 527mm x 296mm
   2560x1440     59.95*+
   1920x1200     59.95  
   2048x1080     60.00  
   1920x1080     60.00    50.00    59.94  
   1600x1200     60.00  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
DisplayPort-3 disconnected (normal left inverted right x axis y axis)

My laptop screen is turned off and I am using the two 2560x1440 screens that are "connected" to DisplayPort-1 and DisplayPort-2.

------

Then I unplug the USB-C connector or the docking station, which automatically turns on the laptop screen. The docking station is no longer connected. (In case you go somewhere with the laptop).

Then I plug the USB-C docking station back in and the screens are connected again.

This time the xrandr output shows the following:

Screen 0: minimum 320 x 200, current 5120 x 1440, maximum 16384 x 16384
eDP connected 1920x1080+0+0 (normal left inverted right x axis y axis) 344mm x 194mm
   1920x1080     60.00*+
   1680x1050     60.00  
   1280x1024     60.00  
   1440x900      60.00  
   1280x800      60.00  
   1280x720      60.00  
   1024x768      60.00  
   800x600       60.00  
   640x480       60.00  
HDMI-A-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-1 disconnected primary (normal left inverted right x axis y axis)
DisplayPort-2 disconnected (normal left inverted right x axis y axis)
DisplayPort-3 connected 2560x1440+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
   2560x1440     59.95*+
   1920x1200     59.95  
   2048x1080     60.00  
   1920x1080     60.00    50.00    59.94  
   1600x1200     60.00  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
DisplayPort-4 connected 2560x1440+2560+0 (normal left inverted right x axis y axis) 527mm x 296mm
   2560x1440     59.95*+
   1920x1200     59.95  
   2048x1080     60.00  
   1920x1080     60.00    50.00    59.94  
   1600x1200     60.00  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
DisplayPort-5 disconnected (normal left inverted right x axis y axis)

As you can see, the two 2560x1440 displays are now connected to DisplayPort-3 and DisplayPort-4.
When I unplug the USB-C docking station again and plug it back in, I still get the same xrandr output.

The question now is why the connection on the DisplayPorts changes. Basically and as logical I feel that the previous configuration would be restored.
Unfortunately, I cannot understand why DisplayPort-3 and DisplayPort-4 are now connected although nothing has changed on the docking station itself.

The EDID of the screens has remained the same. Nothing has changed in this respect.

Thanks
Regards

Last edited by LinuxFan84 (2022-05-29 16:04:56)

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