https://bugs.kde.org/show_bug.cgi?id=468262
Bug ID: 468262
Summary: Dual-DisplayPort monitor only shows image on half of
the screen
Classification: Plasma
Product: KScreen
Version: 5.27.4
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: common
Assignee: kscreen-bugs-n...@kde.org
Reporter: kde....@axhxrx.com
Target Milestone: ---
Created attachment 157939
--> https://bugs.kde.org/attachment.cgi?id=157939&action=edit
screen shot of malfunction
SUMMARY
After updating to KDE Plasma 5.27.4, the Dell UP3218K monitor no longer
displays an image on the entire screen. Instead, it displays an image in a
rectangle that is half the size of the screen.
STEPS TO REPRODUCE
1. Upgrade to KDE Plasma 5.27.4
2. Log in using "KDE Plasma (Wayland)"
3. Look at the monitor
OBSERVED RESULT
The monitor only displays an image within a rectangle that is half of the
screen size (photo attached).
EXPECTED RESULT
The monitor should display an image on the entire display. (This was the result
in KDE Plasma 5.27.3, and at least several previous versions.)
SOFTWARE/OS VERSIONS
Fedora 37 (KDE spin)
KDE Plasma Version: 5.27.4
KDE Frameworks Version: 5.104.0
Qt Version: 5.15.8
GPU: amdgpu (AMD RADEON RX 6600)
ADDITIONAL INFORMATION
This is the Dell UP3128K display, which is one of those older models that uses
2 DisplayPort cables to connect, and although it is a single 8K monitor, it is
made up of two 4K panels. The left and right half of the monitor appear as two
different screens in the "Display Configuration" pane of the System Settings
application.
Prior to KDE Plasma 5.27.4, these can be arranged side by side, so the entire
display can be used. Windows can be displayed normally, even if the window
occupies space on both of the screens.
Because the left half and the right half of this monitor are regarded as two
different screens, the default panel will by default appear on only one half of
the monitor (because it is only supposed to show on one screen), and likewise
maximizing a window will cause it to occupy only half of the physical monitor
(because zooming only considers a single screen) and so forth. These are normal
limitations of using this monitor with most desktop environments.
It might be suspected, but is not the case, that the regression under
discussion here involves using only one of the two panels in the monitor. In
fact, the visual area that the image shows on spans both panels and it centered
on the physical monitor. That is, the left (or right, I actually cannot tell)
screen that is supposed to be on one panel on one half of the monitor is
instead centered, displaying on half of each 4K panel, while the other screen
does not appear at all.
Disabling one of the two "Dell Inc DELL UP3218K" screens and leaving the other
enabled causes the monitor to go black. Reversing that shows an image, so it
seems only one of the two screens is actually capable of producing an image on
the monitor.
REPRODUCTION AND DEBUGGING
I confirmed the expected behavior by rolling back the machine in question to
the previously-installed OS snapshot, which is Fedora 37 with KDE Plasma 5.27.3
and everything works as expected. I also tested with Fedora 38 beta with GNOME,
and it also drives the monitor without a problem. So I believe the monitor and
GPU are working correctly.
I also tried logging into the KDE Plasma 5.27.4 using X11 instead of Wayland.
Although X11 is not very usable in the multi-monitor setup that I normally use,
if one ignores the usual X11 jank/freakout thing where it flashes monitors on
and off in an apparent hallucinatory fugue state for a considerable period of
time, it does eventually drive the displays and show the desktop on them.
However, I confirmed that this same regression is present in KDE Plasma 5.27.4
using X11, and is not specific to Wayland.
Duplicating this hardware configuration is probably difficult, but I would be
happy to help collect diagnostic information or test any potential fixes using
the hardware I have.
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