I had to downgrade both ddcutil and powerdevil to get it to work again. The last known working combination is:

ddcutil-1.4.1-1 (downgraded from ddcutil-2.0.0-1)
powerdevil-5.27.9-1 (downgraded from powerdevil-5.27.9-2)

sudo pacman -U https://archive.archlinux.org/packages/d/ddcutil/ddcutil-1.4.1-1-x86_64.pkg.tar.zst https://archive.archlinux.org/packages/p/powerdevil/powerdevil-5.27.9-1-x86_64.pkg.tar.zst

*** Bug 476369 has been marked as a duplicate of this bug. ***

The only substantive change in 5.27.9 compared to 5.27.8 is https://invent.kde.org/plasma/powerdevil/-/commit/d176188ff9b573a784905cada8824897af86b34b, which doesn't look related to me (but I could be wrong; CCing the author).

Folks who are affected, are you able to make it work again by downgrading only ddcutil and keeping powerdevil the same? Don't forget to reboot afterwards. :)

I can't reproduce this with the given versions of ddcutil and powerdevil.

(In reply to Nate Graham from comment #3)
> The only substantive change in 5.27.9 compared to 5.27.8 is
> https://invent.kde.org/plasma/powerdevil/-/commit/
> d176188ff9b573a784905cada8824897af86b34b, which doesn't look related to me
> (but I could be wrong; CCing the author).
> 
> Folks who are affected, are you able to make it work again by downgrading
> only ddcutil and keeping powerdevil the same? Don't forget to reboot
> afterwards. :)

Thanks for the prompt response Nate. To answer your question:

I've combined the current stable versions (with ddcutil downgraded and using the latest powerdevil), yet the problem persists.
ddcutil version: 1.4.1-1
powerdevil version: 5.27.9-2

Interestingly, I found that only by rolling back to powerdevil 5.27.9-1 did things function properly.

Even though I tried various versions of ddcutil (up to the latest) in tandem with earlier powerdevil versions as well, the specific pairing of powerdevil 5.27.9-1 and ddcutil 1.14.1-1 was the sole combination that addressed the problem.

(In reply to Justin Shepherd from comment #8)

> Even though I tried various versions of ddcutil (up to the latest) in tandem
> with earlier powerdevil versions as well, the specific pairing of powerdevil
> 5.27.9-1 and ddcutil 1.14.1-1 was the sole combination that addressed the
> problem.

You can't mix and match different ddcutil/powerdevil versions at will. ddcutil 1.x and 2.x have different ABI, you need to use a powerdevil version that has been compiled with the exact ddcutil version you are using.

(In reply to Antonio Rojas from comment #9)
> (In reply to Justin Shepherd from comment #8)
> 
> > Even though I tried various versions of ddcutil (up to the latest) in tandem
> > with earlier powerdevil versions as well, the specific pairing of powerdevil
> > 5.27.9-1 and ddcutil 1.14.1-1 was the sole combination that addressed the
> > problem.
> 
> You can't mix and match different ddcutil/powerdevil versions at will.
> ddcutil 1.x and 2.x have different ABI, you need to use a powerdevil version
> that has been compiled with the exact ddcutil version you are using.

Thank you for your input.

While I'm not well-versed in the intricacies of ABI's, versioning with powerdevil, and ddcutil, I was addressing Nate's earlier ask to test the latest powerdevil with an older versions of ddcutil.

Mr. Nate, kindly look at this video. I solved it but have since then switched DEs.

This is a workaround, but I do not know how safe it is.

https://www.youtube.com/watch?v=bFSd6QYerRM

Thanks Antonio, that makes sense. So it sounds like the triggering factor here was in fact ddcutil 2.0, but of course we'll need to adapt to whatever change they made to cause this issue anyway.

Natalie or Nicolas, would either of you be able to look into this?

(In reply to Natalie Clarius from comment #4)
> I can't reproduce this with the given versions of ddcutil and powerdevil.

Presumably because I don't have a DDC capable monitor.

People who experience this bug, do you have any setup available with a built-in screen (i.e. a laptop) and could test whether this problem still occurs?

Also, could you please do

> echo "org.kde.powerdevil=true" >> ~/.config/QtProject/qtlogging.ini

to enable more verbose log output for powerdevil and see what the journal says after rebooting.

(In reply to Natalie Clarius from comment #13)
> (In reply to Natalie Clarius from comment #4)
> > I can't reproduce this with the given versions of ddcutil and powerdevil.
> 
> Presumably because I don't have a DDC capable monitor.
> 
> People who experience this bug, do you have any setup available with a
> built-in screen (i.e. a laptop) and could test whether this problem still
> occurs?
> 
> Also, could you please do
> 
> > echo "org.kde.powerdevil=true" >> ~/.config/QtProject/qtlogging.ini
> 
> to enable more verbose log output for powerdevil and see what the journal
> says after rebooting.

I've been experiencing this issue on my desktop with external monitors, but haven't had the issue on my laptop.

(In reply to Natalie Clarius from comment #13)

> > echo "org.kde.powerdevil=true" >> ~/.config/QtProject/qtlogging.ini
No file or folder with that name, I manually created it but not sure if it made a difference.

I figured out the bug  seem to only happen on my LG C9 55" TV because when I plugged in my proper PC monitor powerdevil don't spike CPU and I am able to enter power settings. 

I'll add journalctl -b 0 | grep -i 'powerdevil'  after fresh reboot for both monitors below.

LG OLED TV:

x@zxc ~> journalctl -b 0 | grep -i 'powerdevil'
Nov 04 15:24:17 zxc systemd[692]: Starting Powerdevil...
Nov 04 15:24:17 zxc kded5[816]: kscreen.kded: PowerDevil SuspendSession action not available!
Nov 04 15:24:18 zxc dbus-daemon[529]: [system] Activating service name='org.kde.powerdevil.discretegpuhelper' requested by ':1.44' (uid=1000 pid=915 comm="/usr/lib/org_kde_powerdevil") (using servicehelper)
Nov 04 15:24:18 zxc dbus-daemon[529]: [system] Successfully activated service 'org.kde.powerdevil.discretegpuhelper'
Nov 04 15:24:18 zxc dbus-daemon[529]: [system] Activating service name='org.kde.powerdevil.chargethresholdhelper' requested by ':1.44' (uid=1000 pid=915 comm="/usr/lib/org_kde_powerdevil") (using servicehelper)
Nov 04 15:24:18 zxc dbus-daemon[529]: [system] Successfully activated service 'org.kde.powerdevil.chargethresholdhelper'
Nov 04 15:24:18 zxc dbus-daemon[529]: [system] Activating service name='org.kde.powerdevil.backlighthelper' requested by ':1.44' (uid=1000 pid=915 comm="/usr/lib/org_kde_powerdevil") (using servicehelper)
Nov 04 15:24:18 zxc backlighthelper[957]: org.kde.powerdevil: no kernel backlight interface found
Nov 04 15:24:18 zxc dbus-daemon[529]: [system] Successfully activated service 'org.kde.powerdevil.backlighthelper'
Nov 04 15:24:18 zxc org_kde_powerdevil[915]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
Nov 04 15:24:18 zxc org_kde_powerdevil[915]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
Nov 04 15:24:23 zxc systemd[692]: plasma-powerdevil.service: start operation timed out. Terminating.
Nov 04 15:24:23 zxc systemd[692]: plasma-powerdevil.service: Failed with result 'timeout'.
Nov 04 15:24:23 zxc systemd[692]: Failed to start Powerdevil.
Nov 04 15:24:23 zxc systemd[692]: plasma-powerdevil.service: Consumed 2.744s CPU time.
Nov 04 15:24:23 zxc systemd[692]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 1.
Nov 04 15:24:23 zxc systemd[692]: Starting Powerdevil...
Nov 04 15:24:23 zxc org_kde_powerdevil[1041]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
Nov 04 15:24:23 zxc org_kde_powerdevil[1041]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
Nov 04 15:24:28 zxc systemd[692]: plasma-powerdevil.service: start operation timed out. Terminating.
Nov 04 15:24:28 zxc systemd[692]: plasma-powerdevil.service: Failed with result 'timeout'.
Nov 04 15:24:28 zxc systemd[692]: Failed to start Powerdevil.
Nov 04 15:24:28 zxc systemd[692]: plasma-powerdevil.service: Consumed 2.758s CPU time.
Nov 04 15:24:28 zxc systemd[692]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 2.
Nov 04 15:24:28 zxc systemd[692]: Starting Powerdevil...
Nov 04 15:24:29 zxc org_kde_powerdevil[1426]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
Nov 04 15:24:29 zxc org_kde_powerdevil[1426]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed


Samsung pc monitor:

x@zxc ~> journalctl -b 0 | grep -i 'powerdevil'
Nov 04 15:26:21 zxc systemd[723]: Starting Powerdevil...
Nov 04 15:26:21 zxc dbus-daemon[537]: [system] Activating service name='org.kde.powerdevil.discretegpuhelper' requested by ':1.41' (uid=1000 pid=922 comm="/usr/lib/org_kde_powerdevil") (using servicehelper)
Nov 04 15:26:21 zxc dbus-daemon[537]: [system] Successfully activated service 'org.kde.powerdevil.discretegpuhelper'
Nov 04 15:26:21 zxc dbus-daemon[537]: [system] Activating service name='org.kde.powerdevil.chargethresholdhelper' requested by ':1.41' (uid=1000 pid=922 comm="/usr/lib/org_kde_powerdevil") (using servicehelper)
Nov 04 15:26:21 zxc dbus-daemon[537]: [system] Successfully activated service 'org.kde.powerdevil.chargethresholdhelper'
Nov 04 15:26:21 zxc dbus-daemon[537]: [system] Activating service name='org.kde.powerdevil.backlighthelper' requested by ':1.41' (uid=1000 pid=922 comm="/usr/lib/org_kde_powerdevil") (using servicehelper)
Nov 04 15:26:21 zxc backlighthelper[970]: org.kde.powerdevil: no kernel backlight interface found
Nov 04 15:26:21 zxc dbus-daemon[537]: [system] Successfully activated service 'org.kde.powerdevil.backlighthelper'
Nov 04 15:26:21 zxc org_kde_powerdevil[922]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
Nov 04 15:26:21 zxc org_kde_powerdevil[922]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
Nov 04 15:26:23 zxc kded5[846]: kscreen.kded: PowerDevil SuspendSession action not available!
Nov 04 15:26:25 zxc systemd[723]: Started Powerdevil.
Nov 04 15:26:25 zxc org_kde_powerdevil[922]: org.kde.powerdevil: Handle button events action could not check for screen configuration
Nov 04 15:26:25 zxc org_kde_powerdevil[922]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"

I believe that this may help someone. If you edit the powerdevil.desktop file and do the following

X-systemd-skip=false
X-KDE-autostart-phase=1

the restart loop breaks. It sometimes returns, and then when I restart the system it goes away. It appears to just appear at random. I edited the file directly that exists within xdg. Maybe this is the solution for now?

The file can be found in /etc/xdg/autostart

It is safe to edit this file, yes?

Following the suggestion by Altamush Nayyer Khan of changing powerdevil.desktop section to

X-systemd-skip=false
X-KDE-autostart-phase=1

did work for me on a HP Z4 G4 pc.

Thank you!

I'm on a desktop PC with two monitors in a PRIME setup (Nvidia + Intel) and also was getting the same powerdevil restart loop (which caused micro-freezes every X seconds)

nov 12 09:41:26 HP3400 systemd[580]: plasma-powerdevil.service: start operation timed out. Terminating.
nov 12 09:41:26 HP3400 systemd[580]: plasma-powerdevil.service: Failed with result 'timeout'.
nov 12 09:41:26 HP3400 systemd[580]: Failed to start Powerdevil.
nov 12 09:41:26 HP3400 systemd[580]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 7.
nov 12 09:41:26 HP3400 systemd[580]: Starting Powerdevil...
nov 12 09:41:27 HP3400 org_kde_powerdevil[1338]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
nov 12 09:41:27 HP3400 org_kde_powerdevil[1338]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
nov 12 09:41:32 HP3400 systemd[580]: plasma-powerdevil.service: start operation timed out. Terminating.
nov 12 09:41:32 HP3400 systemd[580]: plasma-powerdevil.service: Failed with result 'timeout'.
nov 12 09:41:32 HP3400 systemd[580]: Failed to start Powerdevil.
nov 12 09:41:32 HP3400 systemd[580]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 8.
nov 12 09:41:32 HP3400 systemd[580]: Starting Powerdevil...
nov 12 09:41:32 HP3400 org_kde_powerdevil[1400]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
nov 12 09:41:32 HP3400 org_kde_powerdevil[1400]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
nov 12 09:41:37 HP3400 systemd[580]: plasma-powerdevil.service: start operation timed out. Terminating.
nov 12 09:41:37 HP3400 systemd[580]: plasma-powerdevil.service: Failed with result 'timeout'.
nov 12 09:41:37 HP3400 systemd[580]: Failed to start Powerdevil.
nov 12 09:41:37 HP3400 systemd[580]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 9.
nov 12 09:41:37 HP3400 systemd[580]: Starting Powerdevil...
nov 12 09:41:38 HP3400 org_kde_powerdevil[1492]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
nov 12 09:41:38 HP3400 org_kde_powerdevil[1492]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
nov 12 09:41:43 HP3400 systemd[580]: plasma-powerdevil.service: start operation timed out. Terminating.
nov 12 09:41:43 HP3400 systemd[580]: plasma-powerdevil.service: Failed with result 'timeout'.
nov 12 09:41:43 HP3400 systemd[580]: Failed to start Powerdevil.
nov 12 09:41:43 HP3400 systemd[580]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 10.
nov 12 09:41:43 HP3400 systemd[580]: Starting Powerdevil...
nov 12 09:41:43 HP3400 org_kde_powerdevil[1536]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
nov 12 09:41:43 HP3400 org_kde_powerdevil[1536]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
nov 12 09:41:48 HP3400 systemd[580]: plasma-powerdevil.service: start operation timed out. Terminating.
nov 12 09:41:48 HP3400 systemd[580]: plasma-powerdevil.service: Failed with result 'timeout'.
nov 12 09:41:48 HP3400 systemd[580]: Failed to start Powerdevil.
nov 12 09:41:48 HP3400 systemd[580]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 11.
nov 12 09:41:48 HP3400 systemd[580]: Starting Powerdevil...
nov 12 09:41:49 HP3400 org_kde_powerdevil[1584]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
nov 12 09:41:49 HP3400 org_kde_powerdevil[1584]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
nov 12 09:41:54 HP3400 systemd[580]: plasma-powerdevil.service: start operation timed out. Terminating.
nov 12 09:41:54 HP3400 systemd[580]: plasma-powerdevil.service: Failed with result 'timeout'.
nov 12 09:41:54 HP3400 systemd[580]: Failed to start Powerdevil.
nov 12 09:41:54 HP3400 systemd[580]: plasma-powerdevil.service: Scheduled restart job, restart counter is at 12.
nov 12 09:41:54 HP3400 systemd[580]: Starting Powerdevil...
nov 12 09:41:54 HP3400 org_kde_powerdevil[1643]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
nov 12 09:41:54 HP3400 org_kde_powerdevil[1643]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
nov 12 09:41:59 HP3400 systemd[580]: plasma-powerdevil.service: start operation timed out. Terminating.
nov 12 09:41:59 HP3400 systemd[580]: plasma-powerdevil.service: Failed with result 'timeout'.
nov 12 09:41:59 HP3400 systemd[580]: Failed to start Powerdevil.

WORKAROUND

Since I have moved over to Manjaro, I downgraded two packages as following (if you are on Arch or Arch-based this will work):

sudo pacman -U https://archive.archlinux.org/packages/d/ddcutil/ddcutil-1.4.1-1-x86_64.pkg.tar.zst https://archive.archlinux.org/packages/p/powerdevil/powerdevil-5.27.9-1-x86_64.pkg.tar.zst

And the problem is solved.

Operating System: Manjaro Linux 
KDE Plasma Version: 5.27.9
KDE Frameworks Version: 5.111.0
Qt Version: 5.15.11
Kernel Version: 6.6.0-1-MANJARO (64-bit)
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-2400 CPU @ 3.10GHz
Memory: 7.7 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 2000
Manufacturer: Hewlett-Packard
Product Name: HP Pro 3400 Series MT

I see no such issue on Fedora 39, which also has ddcutil 2.0.0

For anyone who is still having issues with this, please read this post: https://bbs.archlinux.org/viewtopic.php?id=289979

Although I released a solution, this one appears to be working better. Only the KDE devs can tell whether this solution or mine is safe or not for the people that are facing this issue. I hope this bug is pushed, and fixed quickly as some people that are using KDE might not even know why their system is hitching due to this.

(In reply to Altamush Nayyer Khan from comment #20)
> For anyone who is still having issues with this, please read this post:
> https://bbs.archlinux.org/viewtopic.php?id=289979
> 
> Although I released a solution, this one appears to be working better. Only
> the KDE devs can tell whether this solution or mine is safe or not for the
> people that are facing this issue. I hope this bug is pushed, and fixed
> quickly as some people that are using KDE might not even know why their
> system is hitching due to this.

You should edit the timeout after you have installed these latest versions of powerdevil & ddcutil, because the update resets it to 5s.

Hm, it is working fine as in you get screen brightness now that is working along Night Color.

For the 3 energy options Power Save / Balanced / Performance that do reappear too, the slider will not hold i. e. I don't think it sets them while logged in. However drag that slider where you want it, maybe try a few times :)  then logout and login and the slider is set. Must be working that way, or how do you make sure the option is in fact in tact after the re-login?
If so, this is a workaround I can live with so a while, latest versions, 1 logo-logi required for changed things to come into effect.
No powerdevil cpu hassle or anything. Thanks for mentioning.

I'm on Manjaro KDE Stable 
Kernel 6 1 62

(In reply to holyzolly from comment #21)
> (In reply to Altamush Nayyer Khan from comment #20)
> > For anyone who is still having issues with this, please read this post:
> > https://bbs.archlinux.org/viewtopic.php?id=289979
> > 
> > Although I released a solution, this one appears to be working better. Only
> > the KDE devs can tell whether this solution or mine is safe or not for the
> > people that are facing this issue. I hope this bug is pushed, and fixed
> > quickly as some people that are using KDE might not even know why their
> > system is hitching due to this.
> 
> You should edit the timeout after you have installed these latest versions
> of powerdevil & ddcutil, because the update resets it to 5s.
> 
> Hm, it is working fine as in you get screen brightness now that is working
> along Night Color.
> 
> For the 3 energy options Power Save / Balanced / Performance that do
> reappear too, the slider will not hold i. e. I don't think it sets them
> while logged in. However drag that slider where you want it, maybe try a few
> times :)  then logout and login and the slider is set. Must be working that
> way, or how do you make sure the option is in fact in tact after the
> re-login?
> If so, this is a workaround I can live with so a while, latest versions, 1
> logo-logi required for changed things to come into effect.
> No powerdevil cpu hassle or anything. Thanks for mentioning.

I edited the timeout after I updated. I am not sure what the issue was though. I am still trying to understand what went wrong.

(In reply to holyzolly from comment #21)
> (In reply to Altamush Nayyer Khan from comment #20)
> > For anyone who is still having issues with this, please read this post:
> > https://bbs.archlinux.org/viewtopic.php?id=289979
> > 
> > Although I released a solution, this one appears to be working better. Only
> > the KDE devs can tell whether this solution or mine is safe or not for the
> > people that are facing this issue. I hope this bug is pushed, and fixed
> > quickly as some people that are using KDE might not even know why their
> > system is hitching due to this.
> 
> You should edit the timeout after you have installed these latest versions
> of powerdevil & ddcutil, because the update resets it to 5s.
> 
> Hm, it is working fine as in you get screen brightness now that is working
> along Night Color.
> 
> For the 3 energy options Power Save / Balanced / Performance that do
> reappear too, the slider will not hold i. e. I don't think it sets them
> while logged in. However drag that slider where you want it, maybe try a few
> times :)  then logout and login and the slider is set. Must be working that
> way, or how do you make sure the option is in fact in tact after the
> re-login?
> If so, this is a workaround I can live with so a while, latest versions, 1
> logo-logi required for changed things to come into effect.
> No powerdevil cpu hassle or anything. Thanks for mentioning.

I do not know whether this workaround is safe or not, by the way. I am not sure why this was shipped without testing. I have heard that PowerDevil has been buggy in the past. What else may have gone wrong that caused this bug. I really want to do my part in getting this bug solved.

I have the same problem since the Update of ddcutil and powerdevil and tried all 3 workarounds in the comments. When I edit the desktop file Powerdevil still fails to start a few times but then the loop stops eventually. If I increase the timeout time only the libddcutil errors below are present. With the downgraded versions no error messages occur regarding this bug. So downgrading currently seems the best option for me.

the repeating entries in my systemd journal log with Powerdevil 5.27.9-2 and ddcutils 2.0.0-1:

Nov 20 16:18:43 xxx systemd[745]: Failed to start Powerdevil.
Nov 20 16:18:43 xxx systemd[745]: plasma-powerdevil.service: Failed with result 'timeout'.
Nov 20 16:18:43 xxx systemd[745]: plasma-powerdevil.service: start operation timed out. Terminating.
Nov 20 16:18:42 xxx libddcutil[15006]: busno=6, sleep-multiplier =  2,00. Testing for supported feature 0x10 returned Error_Info[DDCRC_RETRIES in ddc_write_read_with_retry, causes: DDCRC_DDC_DATA(10)]
Nov 20 16:18:40 xxx libddcutil[15006]: busno=3, sleep-multiplier =  2,00. Testing for supported feature 0x10 returned Error_Info[DDCRC_RETRIES in ddc_write_read_with_retry, causes: DDCRC_READ_ALL_ZERO(10)]
Nov 20 16:18:38 xxx org_kde_powerdevil[15006]: org.kde.powerdevil: org.kde.powerdevil.backlighthelper.brightness failed
Nov 20 16:18:38 xxx org_kde_powerdevil[15006]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"

I experimented a bit with ddcutil and got these infos:

'ddcutil detect' in version 1.4.1
    No /dev/i2c devices exist.
    ddcutil requires module i2c-dev.

'ddcutil detect' in version 2.0.0 (i removed my monitor details)
    Invalid display
    I2C bus:  /dev/i2c-3
    DRM connector:           card0-HDMI-A-1
    EDID synopsis:
        Mfg id:               xxx
        Model:                xxx
        Product code:         xxx
        Serial number:
        Binary serial number: xxx
        Manufacture year:     xxx
    DDC communication failed. (getvcp of feature x10 returned Error_Info[DDCRC_RETRIES in ddc_write_read_with_retry, causes: DDCRC_READ_ALL_ZERO(10)])
    DRM reports the monitor is disabled.

    Invalid display
    I2C bus:  /dev/i2c-6
    DRM connector:           card0-DP-2
    EDID synopsis:
        Mfg id:               xxx
        Model:                xxx
        Product code:         xxx
        Serial number:        xxx
        Binary serial number: xxx
        Manufacture year:     xxx
    DDC communication failed. (getvcp of feature x10 returned Error_Info[DDCRC_RETRIES in ddc_write_read_with_retry, causes: DDCRC_DDC_DATA(10)])
    DRM reports the monitor is disabled.

It looks like ddcutils 2.0 now also lists my previously not recognized displays and prints that communication error. 'ddcutil vcpinfo' says that 'feature x10' is the brightness control support. Since both my monitors don't support that feature, i think that error message is probably correct. But maybe this error could be the reason why Powerdevil fails to start, since it also shows up in my systemd journal shortly before Powerdevil fails.

Can you successfully change your Power Profile whilst in session? @ Altamush Nayyer Khan

(In reply to holyzolly from comment #26)
> Can you successfully change your Power Profile whilst in session? @ Altamush
> Nayyer Khan

After powerdevil starts with the timeout fix, I can change power profiles without a problem.

Now after another relogin, brightness and power levels don't work anymore, also I noticed blocking sleep & screen locking in the Systray menu only work if I apply it a second time?
I disabled auto-dim which with this update gets enabled by default 5min.
I applied your powerdevil.desktop workaround on top.
I will tell reboot and tell the outcomes, next try again with only the timeout edit, try again with  your powerdevil.desktop workaround.
Repeat these steps with the Stable update roll of Manjaro.
If all fails I will downgrade again.
Might take me a while and some ease but I will give feedback.

While hopin' this gets fixed in the meanwhile.

Maybe me not changing to another Activity caused me to think almost all was worked around before. Now I have and relogins don't change anything about the features.

(In reply to holyzolly from comment #29)
> Maybe me not changing to another Activity caused me to think almost all was
> worked around before. Now I have and relogins don't change anything about
> the features.

I do not understand. Has the temporary fixed work or not?

Have you also seen an increase in boot times. After these fixes, the boot time seems to increase. It is noticeable! Boot is probably 10 seconds slower. Windows 10 boots faster right now for me.

I only did the timeout-edit fix then rebooted. It's worked for a while. While I had to relogin to apply power levels (eg power save <> performance), the only downside. Now everything, incl. brightness-adjust won't work. You said you had to reboot once a while to keep it working?

I edited the powerdevil.desktop file now. I had not done that yet. And I have not rebooted yet so can't speak about differences in boot time.

No I didn't notice any difference in boot time.

Maybe some more logs are needed for Natalie to look into. So please if you can provide these logs like shown above, please do.

I have tried all possible working-around possibilities:
Both file edits at the same time. > Brightness slider working at first, you can not set Power Profile (not changed after a re-login, either).
5s changed to 9s. > Brightness slider working at first, you can not set Power Profile (not changed after a re-login, either).
powerdevil.desktop  edit  > Brightness slider working at first, you can not set Power Profile (not changed after a re-login, either).
No edit > Powedevil not shown in Systray so I think it doesn't start

Downgrading the 2 packages > Powerdevil works as expected, but no brightness slider (this feature was introduced with current version)
[I did not try downgrading juust 1 of the 2 packages, these would be 2 more options]
I rebooted each time.

I tried all the above with bot the 23/11/13 and the 23/11/21 stable update cycles of Manjaro. Kernel is 6.1.62

(In reply to holyzolly from comment #32)
> No I didn't notice any difference in boot time.
> 
> Maybe some more logs are needed for Natalie to look into. So please if you
> can provide these logs like shown above, please do.
> 
> I have tried all possible working-around possibilities:
> Both file edits at the same time. > Brightness slider working at first, you
> can not set Power Profile (not changed after a re-login, either).
> 5s changed to 9s. > Brightness slider working at first, you can not set
> Power Profile (not changed after a re-login, either).
> powerdevil.desktop  edit  > Brightness slider working at first, you can not
> set Power Profile (not changed after a re-login, either).
> No edit > Powedevil not shown in Systray so I think it doesn't start
> 
> Downgrading the 2 packages > Powerdevil works as expected, but no brightness
> slider (this feature was introduced with current version)
> [I did not try downgrading juust 1 of the 2 packages, these would be 2 more
> options]
> I rebooted each time.
> 
> I tried all the above with bot the 23/11/13 and the 23/11/21 stable update
> cycles of Manjaro. Kernel is 6.1.62

I can provide the logs is someone tells me how to, since I don't know. I adjust my screen brightness by just adjusting my monitor. I would like to help this get solved.

Might this be distro or driver related?
I have the issue on Manjaro Stable with Nvidia 535 with 3 or 4 monitors
I don't have issue on my Manjaro Stable laptop with Nvidia 390