rockowitz
PHL 242G5 incorrect brightness set
DDCUtil 2.2.1 on manjaro
Problematic monitor is PHILIPS 242G5 where it keeps going what seems to be full brightness. Checking the monitor brightness through the monitors control panel shows unchanged brightness since I last set it manually. Changing the brightness by just 1 point up/down somehow "refreshes" the setting and the brightness is set to what I'd expect the value to be. After a short yet random while it goes back to the full brightness.
I tried disabling the power daemon which I assume sets the screen brightness, but that prevents the computer from sleeping.
ddcutil interrogate attached
(also, dumping the whole journal in the log seems overly excessive)
When you write "checking the monitor brightness through the monitors control panel" are you referring to the On Screen Display, the KDE Brightness and Color widget in the system tray, or something else?
Does the problem occur when you use command line ddcutil?
Does the problem persist if PowerDevil's use of libddcutil is disabled by setting environment variable POWERDEVIL_NO_DDCUTIL=1. (For details see e.g. the PowerDevil README. For a similar problem see e.g. PowerDevil is resetting my display brightness after display wakes up.
The Philips monitor appears at both /dev/i2c-3 and /dev/i2c-9. The behavior has been observed when DisplayPort Multi-Stream-Transport is being used. Are you dasiy chaining monitors?
My best guess is that PowerDevil is resetting brightness to an incorrect value. If you are not using KDE Plasma 6.4, try updating to that version. The beta version of KDE Plasma 6.5 is due out mid-September. PowerDevil has seen a lot of work.
Have you tried connecting the Phillips monitor using HDMI instead of DisplayPort?
Answer to the first question is, the on screen display of the monitor.
Using 'ddcutil setvcp 10 20' for example, updates the brightness correctly on the monitor. This also sets the On Screen Display setting value to whatever I pass to it.
I did however remember that this specific monitor is connected with a Displayport-to-HDMI converter cable. So if this is detected as a daisy-chain through a converter chip, then I'm guessing the cable is the issue.
I am a bit limited in what I use to connect my monitors but I shall try using a different non-converter cable and see if that does help.
On another note, since the brightness does work through ddcutil commandline, I'm guessing the issue is with powerdevil?
Interestingly the issue persists even after setting the environment variable disabling ddcutil from powerdevil.
I may try the manual kde update later since it is a still a beta.
One further thing to try is using ddctui to change brightness value. It uses libddcutil, as does PowerDevil, but takes the latter out of the equation.
To be sure that PowerDevil is not using libddcutil, check in syslog (journalctl -t org_kde_powerdevil). That will show trace information from both PowerDevil and libddcutil. For good measure, put the following line into ~/.config/dddutil/ddcutilrc
option: --trcfunc ddci_set_non_table_vcp_value_verify
That function (indirectly) gets called by any API function that changes a non-table feature value such as x10.
Installed ddcui and all the brightness values set correctly through that, as the cmdline ddcutil does.
I did look into how to update powerdevil itself, but it seems I would be required to build it myself, and the build process seems a tad complex. So updating that myself is not something I am able to do.
I looked for the ~/.config/ddcutil/ddcutilrc file, but there was none, so I created it with the line you gave. I am unsure if this file requires anything else. I also assume that the folder was supposed to be "ddcutil" and not "dddutil"? (neither folder exist by default for me)
As a test I re-enabled ddcutil usage by commenting the environment variable for powerdevil, this reminded me that one of my other monitors gets it's black-level setting set, instead of brightness... (The Fujitsu B24W-6 LED) So disabled ddcutil usage in powerdevil again.
I'm still puzzled as to why the brightness is still being set, however much less often than before. So either the powerdevil toggle does not work or there is something else using ddcutil incorrectly?