Heads up: Kernel 6.1-rc# might break backlight control on old/weird laptops

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Red Hat developer Hans De Goede was recently refactoring the backlight detection code for kernel 6.1, and noticed that some laptops may lose the ability to control their backlight as a result. If you are using a laptop, it is recommended that you check the output of the following command:

ls /sys/class/backlight/

If it shows only one entry such as “intel_backlight”, “nouveau_bl”, “amdgpu_bl0” or “radeon_bl0” then your laptop might be affected - as such it is recommended to adding this parameter to the kernel command line: [HOW TO ADD KERNEL PARAMETERS]

acpi_backlight=video

after which you should check /sys/class/backlight/ again. If an “acpi_video0” entry appears in the ls output, then you’re in the clear. If not, you have a laptop which is likely affected by the upcoming change.

If so, run the following commands:


    ls /sys/class/backlight > ls-backlight.txt

    sudo dmesg > dmesg.txt

    sudo dmidecode > dmidecode.txt

    sudo acpidump -o acpidump.txt

And send an email about this at hdegoede@redhat.com with the 4 generated .txt files attached.

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