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


If you’re lazy and don’t want to click on the link…
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]


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.