Have you got a “very old” or “strange in any other manner” laptop? Did it come pre-installed with Windows, or did you use coreboot to flash the firmware? You may assist the Linux kernel in improving its backlight code without giving up on oddball equipment like yours.
De Goede is starting some significant improvements to user-space lighting controls, which he has been working on since 2014. As a result, he needs old laptop tests. There are numerous problems with how Linux attempts to accommodate the huge range of illumination schemes in screens, as de Goede brought out at the recent Linux Plumbers Conference, as described by the Linux blog Phoronix. A single display may be powered by various backlighting systems, leaving high-level controls to “guess which one will work.” Right now, root access is needed for brightness control. As the engineer noted in 2014, “0” handed down as a backlight value is still puzzling: Is that completely dark, or dim as the display can go?
With the adjustments de Goede has suggested for kernel 6.1, it would be possible to specify the maximum brightness levels, make it evident when brightness controls are not supported, and react to hotplug events like connecting a monitor with a different brightness control scheme.
You can see if your (ancient, strange) laptop might be affected by executing ls /sys/class/backlight if it already runs Linux or if you can boot it into a live USB session. There is a potential that the significant impending backlight update may have an impact on your laptop if there is just one entry and it is labeled intel backlight, nouveau bl, amdgpu bl0, or radeon bl0. Follow the directions in de Goede’s post to conduct additional testing.
It can be challenging to write the correct code to properly power a laptop display, as was demonstrated in a recent emergency update to the Linux kernel. The creators and maintainers of the kernel are unable to test all of the laptop displays that are currently available. You might be able to assist if you have an old computer that can boot into Linux.