https://bugs.kde.org/show_bug.cgi?id=434604
Bug ID: 434604
Summary: Multiple monitor configuration gets broken
Product: plasmashell
Version: master
Platform: Kubuntu Packages
OS: Linux
Status: REPORTED
Severity: major
Priority: NOR
Component: Multi-screen support
Assignee: aleix...@kde.org
Reporter: dan...@wolstenholme.net
CC: plasma-b...@kde.org
Target Milestone: 1.0
SUMMARY
I have a Dell E6440 laptop with a dual-monitor docking station, with two
monitors connected to it via mini-DisplayPort. I recently upgraded both
monitors (but separately, I bought one, then a couple weeks later got another).
Between various unplugging and re-plugging of all the different monitors, I
saw multiple problems where, when a particular monitor was plugged in, the
system would simply not use that monitor, and would continually say a new
monitor was plugged in, then quickly say a monitor has been unplugged, over and
over endlessly. It seemed like one of my monitors had gone bad. But then I saw
the same thing with one of the new monitors.
I was able to debug this problem, and determined that the screen configuration
was being stored in ~/.local/share/kscreen (which I found odd, and made it
really hard to find this, because it seems like most KDE config stuff is in
~/.config these days). In that directory is one randomly-named JSON file with
entries for all the connected monitors, including their ID number, name,
refresh rate, size, and position, and other info. In the "outputs"
subdirectory within this directory are files named with those ID numbers, and
containing basically the exact same info.
What I found ultimately was that, in the top-level file, there was still an
entry for one of my old monitors, and in addition (and I believe this was the
actual source of the bug), my two new monitors had the same name (they were
both called "DP-1").
I cleaned up this directory, deleting the references to the old monitor, and
renaming the two new monitors so they had unique names ("DP-1" and "DP-2", and
"eDP-1" for the laptop's screen), and restarted. Ever since then, I haven't
had any trouble, though I have not yet tried undocking and redocking, or
unplugging and re-plugging the monitors.
It seems to me that what's needed here is for some logic to ensure that any
newly-detected monitor does not have the same name as any other that's already
been detected, or if such logic exists, there must be some bug with it.
STEPS TO REPRODUCE
1. Plug in 2 monitors
2. Unplug one, plug in a 3rd
3. Play around with unplugging and replugging the monitors, using different
ports
OBSERVED RESULT
System will refuse to use one of the monitors, and constantly change
configuration as if a monitor is being plugged in and immediately unplugged 2
seconds later.
EXPECTED RESULT
System should be able to handle any combination of monitor plugging and
unplugging into any port.
SOFTWARE/OS VERSIONS
Windows:
macOS:
Linux/KDE Plasma: Kubuntu 20.04.2
(available in About System)
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.4.0-67-generic
ADDITIONAL INFORMATION
Dell Latitude E6440, Radeon GPU
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