Brightness controls/OSD/powerdevil occasionally fail to see external display

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1

I’m talking about this guy here:

image

Often it shows both the internal and external display, which is an iiyama ProLite XUB2493QSU (plasma shows it as PL2493Q), and it supports DCC and it’s also enabled from the display’s OSD.

Yet sometimes when I use the brightness shortcuts on my keyboard, only the laptop display changes brightness - the external one is nowhere to be seen, not even in the brightness widget in my tray.

Is there anything I can check in the logs? A systemd service or something?

Thanks!

❯  journalctl -b | grep org_kde_powerdevil | grep ddc
Hint: You are currently not seeing messages from other users and the system.
      Users in the 'systemd-journal' group can see all messages. Pass -q to
      turn off this notice.
Dec 05 09:05:06 andromeda org_kde_powerdevil[2412]: Initializing libddcutil.  ddcutil version: 2.1.4, shared library: /usr/lib64/libddcutil.so.5.1.2
Dec 05 09:05:07 andromeda org_kde_powerdevil[2412]: busno=14, Feature 0xdd should not exist but ddc_get_nontable_vcp_value() succeeds, returning mh=0x00 ml=0x64 sh=0x00 sl=0x64
Dec 05 09:05:07 andromeda org_kde_powerdevil[2412]: busno=14, Feature 0x41 should not exist but ddc_get_nontable_vcp_value() succeeds, returning mh=0x00 ml=0x64 sh=0x00 sl=0x64
Dec 05 09:05:07 andromeda org_kde_powerdevil[2412]: busno=14, Feature 0x00 should not exist but ddc_get_nontable_vcp_value() succeeds, returning mh=0x00 ml=0x64 sh=0x00 sl=0x64
Dec 05 13:02:39 andromeda org_kde_powerdevil[2412]: org.kde.powerdevil: [DDCutilDisplay]: ddca_open_display2 -3030
Dec 05 13:02:40 andromeda org_kde_powerdevil[2412]: org.kde.powerdevil: [DDCutilDisplay]: ddca_open_display2 -3030
Dec 05 13:02:42 andromeda org_kde_powerdevil[2412]: org.kde.powerdevil: [DDCutilDisplay]: ddca_open_display2 -3030
Dec 05 13:02:45 andromeda org_kde_powerdevil[2412]: org.kde.powerdevil: [DDCutilDisplay]: ddca_open_display2 -3030
2

you can try installing gddccontrol for perhaps better access to both monitor’s controls

the slider in the brightness control is still a work in progress, imho.

if you have reproducible condition/glitch, please file a bug report.

3

Thanks a lot for this, my distro (tumbleweed) doesn’t provide that package, but I got ddcutil instead and it’s pretty straightforward (I ended up using tldr ddcutil which provided wonderful pre-made examples).

With this I proved that the communication with the display itself is still OK, so it’s not a kernel/driver or display issue, it’s really KDE that somehow loses access to it.

I’ll report a bug

EDIT:
I think there’s already a few:

https://bugs.kde.org/show_bug.cgi?id=482713
https://bugs.kde.org/show_bug.cgi?id=495819

https://bugs.kde.org/buglist.cgi?quicksearch=brightness%20controls&list_id=2936789

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