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/intel_backlight/ disappeared

Going strong on my laptop runit install for circa 2 years. Lenovo X390 Yoga fwiw.

Using backlight_control with Awesome WM keybindings to control screen brightness.

In the past week however, /sys/class/backlight/intel_backlight/ has disappeared

I now only have an empty directory at /sys/class/backlight/

searched around a bit and see that a disappearing intel_backlight directory has happened to others on Arch and Ubuntu. Have not yet found an explanation for how this can happen, nor how to fix it.

Any ideas?  Currently without any ability to control screen brightness. Would like to fix, but almost as much, to know how it happened 

Thank you for your time

Re: /intel_backlight/ disappeared

Reply #1 –
Apparently the 6.1 kernel needs an addition kernel option to use the back light as per the options shown on Arch wiki backlight entry.
Quote
Kernel command-line options
Sometimes ACPI does not work well due to different motherboard implementations and ACPI quirks. This results in, for instance, inaccurate brightness notifications. This includes some laptops with dual graphics (e.g., Nvidia/Radeon dedicated GPU with Intel/AMD integrated GPU). Additionally, ACPI sometimes needs to register its own acpi_video0 backlight even if one already exists (such as intel_backlight), which can be done by adding one of the following kernel parameters:
Code: [Select]
acpi_backlight=video
acpi_backlight=vendor
acpi_backlight=native
If you find that changing the acpi_video0 backlight does not actually change the brightness, you may need to use acpi_backlight=none.

One of the kernel line "acpi_backlight" options needs to be added to whatever boot loader you use.
Or one can try the "system/linux-lts 5.15.86-1" which does not require any kernel line options for the back light to function.

Re: /intel_backlight/ disappeared

Reply #2 –
I guess this is related to "recent" rewrite of backlight things in 6.1 kernel.
For test I recommend going back to linux-lts (5.15) and contacting the guy who worked on it.

My information comes from:
https://www.phoronix.com/news/Linux-Laptop-Brightness-More
https://www.phoronix.com/news/Linux-6.1-Old-Laptop-Backlights
https://www.phoronix.com/news/2022-Linux-Backlight-Overhaul
https://hansdegoede.livejournal.com/26427.html

Re: /intel_backlight/ disappeared

Reply #3 –
Quote from: SGOrava – on
I guess this is related to "recent" rewrite of backlight things in 6.1 kernel.
For test I recommend going back to linux-lts (5.15) and contacting the guy who worked on it.

My information comes from:
https://www.phoronix.com/news/Linux-Laptop-Brightness-More
https://www.phoronix.com/news/Linux-6.1-Old-Laptop-Backlights
https://www.phoronix.com/news/2022-Linux-Backlight-Overhaul
https://hansdegoede.livejournal.com/26427.html

Thanks for this, read de Groede's posts on this and think there may not be an easy fix. Weird because my laptop is still quite new and this issue mostly affected old hardware. I will try switching kernels in the next few days and test