Radeon Linux Driver Preparing Adaptive Backlight Management (ABM)
Adaptive Backlight Management reduces the backlight level in an effort to save power but increases the pixel contrast and luminance to improve image quality and readability under the lower light condition.
The ABM reacts dynamically based upon the pixel luminance of the content being displayed on the screen and works with eDP displays and supported GPUs. This functionality relies upon a "DMCU" firmware that is currently only available for Raven Ridge hardware.
To end-users, the ABM functionality can be controlled as a DRM property and four different values ranging from small power-savings to maximum power-savings with the greatest backlight reduction and most extreme contrast increase.
This functionality is currently being plumbed into the AMDGPU kernel driver and presumably will make it in time for the Linux 4.21 cycle in early 2019. Again though this Adaptive Backlight Management will only work for eDP outputs with (currently) Raven Ridge APUs and does require the latest firmware support too.