SUMMARY

PowerDevil periodically pokes DPMS while the screen is off, causing USB hub devices to briefly wake, even when no user activity occurs.  This bothers me because I have connected a back light (and my mouse) to the usb hub of my monitor, so powering it on causes blips in the backlight.

STEPS TO REPRODUCE
    1 Login to Plasma 6 on X11 or Wayland.
    2 Lock the screen with Ctrl–Alt–L.
    3 Let the monitor enter DPMS-off state.
    4 Wait ~25 seconds — the monitor briefly wakes (1–2 s), and the USB hub devices power on.
    5 Start audio playback (e.g., Audacious); the blips stop immediately.
    6 Stop audio playback; blips resume.

OBSERVED RESULT
    DPMS briefly toggled every ~25 s when no audio is playing.
    USB hub devices wake during these short DPMS pulses.
    No logging appears in journalctl --user or via dbus-monitor.

EXPECTED RESULT
    Once the screen is off via DPMS, it should remain off until user activity.
    PowerDevil should not trigger brief wake pulses that affect USB hubs.


SOFTWARE/OS VERSIONS
Debian Trixie
Linux/KDE Plasma: 4:6.3.6
KDE Plasma Version: 4:6.3.6

ADDITIONAL INFORMATION
    I did see this kind of blibs on Plasma5 (Debian Bookworm), but not nearly as often. Maybe a few times in an hour.

    Editing ~/.config/powermanagementprofilesrc to set [AC][DimDisplay] idleTime=0 stops the blips.

    The blips are suppressed while audio is playing, suggesting the DPMS timer is internally inhibited by active audio streams.

    No D-Bus or external signals trigger these DPMS pokes; it seems to occur entirely inside PowerDevil’s timers.

   This happens on my BenQ PD3200U monitor

Suggestions:
    The internal PowerDevil idle timer should not touch DPMS when the screen is already off.
    Consider separating “monitor off” checks from periodic timers that can wake USB devices unnecessarily.