Do you have a laptop that’s either “pretty old” or “otherwise weird”? Did it come from the factory without Windows or did you flash the firmware with Coreboot? They could help the Linux kernel push its backlighting code without sacrificing quirky gear like yours.
Hans de Goede, a longtime Linux developer and chief engineer at Red Hat, writes in his Livejournal about the need to test “a special group of laptops” to prevent their backlight controls from disappearing in the Linux 6.1 kernel.
Legacy laptop reviews are needed as de Goede is initiating some major changes to user space backlight control that he’s been working on since 2014. Backlight schemes in displays that de Goede recently unveiled at the Linux Plumbers Conference. There may be multiple backlight devices serving a single display, requiring the high-level controller to “guess which one works”. Brightness control currently requires root privileges. And the “0” passed as the backlight value remains a mystery, as the engineer pointed out in 2014: Is that all off, or as low as the display can be illuminated?
The changes de Goede proposed for Kernel 6.1 would allow setting maximum brightness values, communicating clearly when brightness controls are not supported, and reacting to hotplug events such as: B. Connecting a monitor that supports a different brightness control scheme.
If your (old, weird) laptop is already running Linux or you can boot it into a live USB session, you can check if your laptop might be affected by running it
ls /sys/class/backlight. If there is only one entry, and it is called
radeon_bl0, chances are your laptop will be affected by the big upcoming backlight change. To test further, follow the instructions in de Goede’s post.
As seen in a recent emergency Linux kernel update, providing the correct code to properly power a laptop display is tricky. There are many laptop displays out there, and kernel authors and maintainers cannot test them all. If you have an old one that you can boot into Linux, maybe you can help.