Join Displays failed when using two external monitor of one Full HD and one Ultra HD

[Shih-Yuan Lee]

[Summary] Join Displays failed when using two external monitor of one Full HD and one Ultra HD

[Reproduce Steps]
1. Boot into the desktop environment with DELL DOCK - WD19 130W [1].
2. Connect one Ultra HD (3840x2160) external monitor and one Full HD (1920x1080) external monitor.
3. Press Win+P to switch to Join Displays mode.

[Results]
Expected: All monitors including the internal monitor can display with Full HD (1920x1080).
Actual: The Ultra HD monitor can not display.

[Additional Information]
1. Using only Ultra HD (3840x2160) external monitor with internal Full HD (1920x1020) display works fine.
2. Executing the command like `xrandr --output eDP-1 --primary --preferred --output DP-1-1 --preferred --left-of eDP-1 --output DP-1-2 --above eDP-1 --mode 1920x1080 --rate 60` can work. (P.S. DP-1-2 is connected to Ultra HD.)

[1] https://www.dellemc.com/resources/en-us/asset/data-sheets/products/electronics-accessories/dell_dock_wd19_130w_spec_sheet.pdf

[Daniel van Vugt (vanvugt)]

Are you able to supply apport info?

  apport-collect 1841886

[Daniel van Vugt (vanvugt)]

Sounds like this?...

  https://gitlab.gnome.org/GNOME/mutter/issues/728

[Shih-Yuan Lee (fourdollars)]

It doesn't look like https://gitlab.gnome.org/GNOME/mutter/issues/728.

It is about the hardware limitation that DELL DOCK - WD19 130W only supports two external Full HD at the same time.
However mutter doesn't know the hardware limitation.

I guest mutter will try to set up external Ultra HD and external Full HD that is over the hardware limitation of DELL DOCK - WD19 130W so it failed.

[Daniel van Vugt (vanvugt)]

Thank you for reporting this bug to Ubuntu.

Ubuntu 18.04 (bionic) reached end-of-standard-support on May 31, 2023.

See this document for currently supported Ubuntu releases:
https://wiki.ubuntu.com/Releases

We appreciate that this bug may be old and you might not be interested in discussing it anymore. But if you are then please upgrade to the latest Ubuntu version and re-test. If you then find the bug is still present in the newer Ubuntu version, please add a comment here telling us which new version it is in.