AMDGPU Backlight class definitions
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Joined: 01 Oct 2023
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Hi all,

I have some backlight issues on a laptop with a Radeon graphics card using the open-source AMDGPU driver.

On every boot, I need to use the kernel parameter "acpi_backlight=native" and echo "1" to /sys/class/backlight/amdgpu_bl?/brightness to have video output. This is not a huge problem, but was difficult to find.

In all of the Linux 6.x kenels I have tested, this class changed from amdgpu_bl0 to amdgpu_bl1 for no apparent reason. Firstly, I needed to change my startup script, but also my backlight-controls disappeared (/sys/class/backlight/gmux_backlight got removed), which means I can no longer control brightness intensity, only on/off.

However, using the Liquorix kernel, the amdgpu_bl0 still stayed the same, even on the latest linux version. Unfortunately, I also have no backlight-control, because there is no gmux_backlight class (I haven't tried the 5.x kernels).

Does anybody have any info at all why this amdgpu_bl class and the card number changed in the "upstream" kernel, why it did not change in the Liquorix kernel and/or if there is any way to bring back the gmux_backlight class using AMDGPU?

I'm interested in any insight on this whatsoever, because I wasn't able to find any info on this.
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Joined: 26 Sep 2003
Posts: 4127
Location: East Coast, West Coast? I know it's one of them.
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Please show inxi -bxz just to confirm the system data.
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