[plasmashell] [Bug 524276] New: Samsung LS27D70xE repeatedly disconnects and reconnects under Plasma

https://bugs.kde.org/show_bug.cgi?id=524276

            Bug ID: 524276
           Summary: Samsung LS27D70xE repeatedly disconnects and
                    reconnects under Plasma
    Classification: Plasma
           Product: plasmashell
      Version First 6.7.4
       Reported In:
          Platform: CachyOS
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: Power management & brightness
          Assignee: [email protected]
          Reporter: [email protected]
  Target Milestone: 1.0

Created attachment 195165
  --> https://bugs.kde.org/attachment.cgi?id=195165&action=edit
bad-display-user.txt: Plasma/PowerDevil user-session log captured while the
Samsung monitor was repeatedly disconnecting and reconnecting.

DESCRIPTION

When using a Samsung LS27D70xE 27-inch 4K monitor over HDMI, the display
repeatedly disconnects and reconnects under Plasma Wayland.

The desktop appears normally for several seconds, then the monitor loses the
display, reconnects, works normally again for a short time, and repeats the
cycle. If left running like this for several cycles, the display session can
become unstable.

PowerDevil logs during the problem showed failed DDC/CI brightness operations
for the Samsung monitor, followed by display disconnect and reconnect events.
KDE also reported "There are no outputs - creating placeholder screen" while
the monitor was disconnected.

A DRM udev capture during reproduction showed repeated HOTPLUG=1 events for the
RX 9060 XT DRM device.

I tested another 27-inch 4K MSI monitor on the same PC and it works normally
without the disconnect/reconnect loop.

The behavior looks similar to KDE Bug 494522, but this is a different Samsung
monitor model.

STEPS TO REPRODUCE

1. Boot CachyOS into Plasma Wayland.
2. Connect the Samsung LS27D70xE to the Radeon RX 9060 XT using HDMI.
3. Wait several seconds after reaching the desktop.

OBSERVED RESULT

The Samsung monitor repeatedly disconnects and reconnects. The desktop displays
correctly between disconnects, but the cycle continues and makes the system
difficult to use.

EXPECTED RESULT

The monitor should remain connected and display the Plasma desktop
continuously.

SOFTWARE/OS VERSIONS

Operating System: CachyOS
Kernel: 7.1.8-1-cachyos
KDE Plasma Version: 6.7.4
Session: Wayland
GPU: AMD Radeon RX 9060 XT 16 GB
Monitor: Samsung LS27D70xE
Connection: HDMI

KDE Frameworks Version: not checked
Qt Version: not checked

ADDITIONAL INFORMATION

PowerDevil logged DDC/CI brightness communication failures around the same time
as the display disconnects.

A different MSI 27-inch 4K monitor works normally on the same machine.

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