Red Hat engineer Hans de Goede has been working on Linux hardware improvements for desktops/laptops for a long time. At the recent Linux Plumbers conference, Hans introduced the latest improvement: user space backlight/brightness interface interface optimization.

Hans has been talking about the backlight interface as early as 2014, and has been working on solving the current API that restricts user space through /sys/class/backlight and introducing a new, better designed API. Because the current backlight uAPI has a lot of problems, such as the inability to map the backlight sysfs device to the display, one display needs to adapt to multiple backlight sysfs devices, the control of brightness requires root permissions, the meaning of 0 value is undefined, etc.

The current latest plan is to add new “display_brightness” and “display_brightness_max” properties to the DRM connector object, and when display_brightness_max == 0, it is defined as not supporting brightness control.

Those who want to know more about this can check out Hans’s LPC 2022 slides (PDF), and his kernel patch to fix the problem.