Old & Weird Laptops Risk Seeing Broken Backlight Controls With Linux 6.1
Red Hat's Hans de Goede has issued a notice that the new kernel may break backlight controls on "old/weird" laptops. This is coming due to Linux 6.1 having landed the big overhaul to Linux's display brightness/backlight interface. This is a big improvement for Linux backlight handling especially for newer hardware, but for older and quirky devices it may cause some initial fallout -- and thus the warning with early call for testing.
Laptops that are either "pretty old" and/or "weird" in that they did not ship with Windows as the default OS, have been flashed with Coreboot or other firmware modifications, or other changes putting the hardware into a more unique position.
While it's most ideal trying out a Linux 6.1 release candidate to look for any signs of trouble, Hans de Goede published a blog post that does outline some steps Linux laptop users can take on existing kernels to see if your laptop(s) are potentially affected.
If your laptop is potentially affected, Hans is collecting /sys/class/backlight, dmesg, dmidecode, and acpidump logs from the hardware to help in addressing the backlight control changes. See Hans' blog for more details on this backlight control change with Linux 6.1 and the risk it poses for older laptops.