KDE Slider Display Backlight in Energy - No effect

incedis

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Slider in Energy for the display backlight in KDE is not producing any effect. It moves but with no effect on the actual display.
Keyboard shortcuts for the display backlight work as expected.
End result is, after reboot/disconnecting and reconnecting external display, backlight is stuck at 100%. Not a show stopper in itself. The keyboard shortcuts allow me to fix the display backlight.
 


kc1di

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Which Distro are you using?
 
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incedis

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Arch. I am distro hopping like crazy at the moment.
My distro of choice was Ubuntu LTS but could not stick with due to touchpad issue.
 

kc1di

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I don't have any back lit screens here at the moment but use MX-21 - KDE and have not had any problems with it.
Might give it a try won't be the latest plasma but it works fine on my hardware here.
 
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incedis

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I am also going back and forth between KDE and Xfce. Having a lot quirks with KDE that dont show with Xfce.
Having said that, besides the backlight display/keyboard slider not being very useful, I have no other issue with KDE. BTW, when I set the display backlight in Xfce, it sticks even after a reboot. Not the case with KDE.
 

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I'm not sure if you're trying to control the backlight of the externally connected display or of a built-in laptop display.

There is a command line solution for external displays: ddcutil (https://www.ddcutil.com/) which employs VESA DDC. I've written a lite system-tray resident GUI for ddcutil: vdu_controls (https://www.ddcutil.com/). Inbuilt displays mostly don't conform to any of the DDC standard, so ddcutil is unlikely to work with them.
 
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incedis

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built in display.
Backlight is now completly messed up again following updates of video and kernel. Keys shortcut work as expected but nothing happens. Stuck at 100 % (built in). Tried everything under the sun but nothing works.
 
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digitaltrails

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built in display.
Backlight is now completly messed up again following updates of video and kernel. Keys shortcut work as expected but nothing happens. Stuck at 100 % (built in). Tried everything under the sun but nothing works.
I get the impression that laptops vary a bit. The arch documentation is usually the most complete and accurate, but I imagine you've already read through that:
https://wiki.archlinux.org/title/backlight
 
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incedis

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Thanks for your reply.. Yes read the arch doc and some more. Its a no go. I am new to Linux but learnt that sometimes, you just need to know how to give up. Or probably let go. I fix some and loose some.. Especially when issue was fixed prior to upgrading kernel/video drivers. This is simply way too complicated for my little brain. I wish I could understand just for sake of understanding and feeling that I am learning something :)
 
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incedis

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I have made a few steps understanding the issue with internal display backlight.
Code:
ls /sys/class/backlight
revealed two modules for backlight
ideapad and nvidia_0.
I am using discrete gpu and not hybrid.
Added to kernel "acpi_backlight=native" and "nvidia.NVreg_RegistryDwords-EnableBrightnessControl=1"
my legion 5 has the internal screen backlight working again.. Don't know for how long but for the moment my eyes can rest :)
The KDE slider still does nothing for me but it isn't a show stopper any ways.
PS: by adding "nvidia.NVreg_RegistryDwords-EnableBrightnessControl=1" the module "ideapad" is not present and nvidia can take over only if you are using the discrete card. I did not install the drivers for the GPU graphic card. Probably part of the issue in the first place !!
 
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incedis

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After many days of testing I found a workaround (I guess) that is quite interesting because the KDE slider now works flawlessly and the keyboard shortcut to decrease or increase the internal display brightness.

Added in /etc/X11/xorg.conf.d/10-nvidia-brightness.conf. No more use of "acpi_backlight=" in GRUB

Code:
Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    Option         "RegistryDwords" "EnableBrightnessControl=1"
EndSection

Strangely enough (strange as in I do not understand) KDE slider and keyboards shortcut now work flawlessly for the internal display..
One caveat, make sure this file is there and not corrupted. Otherwise, you will boot to a blackscreen. Also, I am solely using Nvidia drivers and not the iGPU (amd in my case). In the BIOS I have set it to only boot to the dGPU. If you set it up to boot hybrid, nothing will work as expected.
Hope this help..

Happy 2022 :)

PS: If anyone can tell me why this conf file is now needed to avoid booting to a blackscreen, I would be very happy :)
 
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incedis

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Posting again for Max visibility for those with AMD legion 5 and backlight issue. read this bug --> Bug-Legion5-AMD-Backlight
My workaround is to use the dGPU. As posted in my previous post it works very well by adding "Option RegistryDwords" "EnableBrightnessControl=1" in the nvidia conf file. What I could never figure out, is why I had to create a second file called "10-nvidia-brightness.conf".
 

kc1di

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Glad you found a work around. Wish I could help more but the info seems to be very specific to your particular machine model.
Anyway Glad you stuck with it and found a solution that will work. Enjoy! :)
 
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incedis

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thanks
It still defeat the purpose of having a mobile platform because running only with dGPU is terrible as far as power management. I am getting barely 2hours of runtime. But still I am willing to make this sacrifice because running Windows is simply out of the question at this stage
 

KGIII

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What I could never figure out, is why I had to create a second file called "10-nvidia-brightness.conf".

Speculation:

Those file numbers indicate in which order configuration files are loaded. So, my guess is that you had to create the configuration file to ensure your changes were loaded at the right time.
 
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incedis

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I have two files in /etc/X11/xorg.conf.d/. One is 10-nvidia-brightness.conf and the other one is 20-nvidia.conf.
My first approach was to used the config from 10-nvidia-brightness.conf and edit the 20-nvidia.conf with it..
Restart, boot, password for encrypted drive, and then screen where I would put my password for my user but black screen.
Then I found a post (like 10 years old post) explaining that the config potentially would need to be split with this new file 10-nvidia-brightness.conf. Created the file and put all the config related to brightness.
Restart, boot, passwd for encrypted drive and then screen for user passwd and voila. Why is that ?

Not knowing is hard :)

PS: Actually using the 10-nvidia-brightness.conf for DPI conf. Made a lot of difference as far as quality.
 

KGIII

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Yeah, that sounds about right. The number at the start indicates when it's loaded. You have to load your changes before other configuration options. Why specifically? I'm not sure. Maybe the configuration change you made is overwritten by the configuration file with the higher number?

So, yeah, it makes sense to me.
 
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incedis

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but wouldn't me taking the conf in 10-nvidia and put everything in 20-nvidia do the same. Only one file to be loaded with all the necessary config ? confused ..
Before going down the rabbit hole of display brightness with this specific laptop, I had only one config file. A couple of upgrade (kernel and video) and this is where I am now with two files. I am missing something.
 

KGIII

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but wouldn't me taking the conf in 10-nvidia and put everything in 20-nvidia do the same.

Not if something in that config file prevents your additional configuration from loading. I don't know enough about nvidia's configuration files to say specifically what it might be.
 
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incedis

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ok. thanks. I have been down the nvidia rabbit hole for the past month and its so cooomplicated. :)
I now appreciate the effort put into making a PC !!
 
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