https://bugs.kde.org/show_bug.cgi?id=510077
Bug ID: 510077
Summary: Monitor output order inconsistent when using
Thunderbolt dock
Classification: Plasma
Product: kwin
Version First 6.4.5
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: multi-screen
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
When a Thunderbolt dock with multiple monitors is connected, each time the
system wakes up and connects to the dock, the identity of the monitors may
change. This leads to monitor layout changing (e.g. the monitors swapping
places), custom tiling layouts swapping monitors or disappearing, and related
issues.
STEPS TO REPRODUCE
1. Connect at least two monitors via a Thunderbolt dock (my suspicion is that
USB-C dock will behave the same but I don't have a ready way to test)
2. Configure a monitor layout
3. Put the system to sleep
4. Wake the system up
OBSERVED RESULT
There's a significant change that the two monitors will swap. In fact, it seems
to be more likely than 50%, as oddly enough the two monitors seem to randomly
rotate between more than two "identities." See below.
EXPECTED RESULT
I would expect the monitors to successfully be identified as the same monitors
that were connected when the system was previously awake.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora 42 KDE Plasma Desktop Edition
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
ADDITIONAL INFORMATION
This occurs on an Intel Core 5 Ultra using embedded graphics and the i915
driver. The same problem occurs on previous versions of KDE as well (at least
on 6.3.1).
Below is partial output from "kscreen-doctor -o" run three times, with the
system sleeping and waking between each. I have removed the first output which
is the laptop embedded screen, and a lot of lines for brevity.
Output: 2 DP-2 a4190ae4-f929-47d8-ba94-6dfcff2c5caf
Geometry: 3200,0 3200x1800
Output: 3 DP-3 254ea6ce-56aa-4634-8cd3-a7d4af556d68
Geometry: 0,0 3200x1800
(sleep/wake cycle)
Output: 2 DP-3 254ea6ce-56aa-4634-8cd3-a7d4af556d68
Geometry: 3200,0 3200x1800
Output: 3 DP-2 6ce750ab-ba0d-4cf3-ac95-d8a93999bb56
Geometry: 0,0 3200x1800
(sleep/wake cycle)
Output: 2 DP-3 254ea6ce-56aa-4634-8cd3-a7d4af556d68
Geometry: 0,0 3200x1800
Output: 3 DP-2 6ce750ab-ba0d-4cf3-ac95-d8a93999bb56
Geometry: 3200,0 3200x1800
Note that sometimes we get DP-2 and then DP-3, but sometimes we get DP-3 and
then DP-2. Further, despite there being two monitors, we see at least three
different GUIDs. There seem to be three different saved custom tiling layouts
to match. I think two different things are happening: first, the order of the
monitors in terms of output numbers is random rather than deterministic.
Second, something is sometimes happening that causes KDE to think that one of
the monitors is a totally different monitor than it was before.
I would be happy to provide more information, I'm not sure what else would be
useful for diagnostics. I did find the following interesting in dmesg, from the
same sleep/wake cycles as above.
[ 164.524808] rc rc0: DP-3 as /devices/pci0000:00/0000:00:02.0/rc/rc0
[ 164.524839] input: DP-3 as /devices/pci0000:00/0000:00:02.0/rc/rc0/input22
[ 164.707432] rc rc1: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1
[ 164.707459] input: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1/input23
[ 170.268142] rc rc1: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1
[ 170.268172] input: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1/input34
[ 1005.010674] rc rc1: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1
[ 1005.010704] input: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1/input35
[ 1138.544100] rc rc1: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1
[ 1138.544129] input: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1/input36
[ 1310.053770] rc rc1: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1
[ 1310.053797] input: DP-2 as /devices/pci0000:00/0000:00:02.0/rc/rc1/input37
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