brightness is controlled by vendor specified hotkey. And there is no interface for OS to adjust brightness.
brightness could be controlled by ACPI
ACPIIt is often possible to adjust the backlight by ACPI. This controls the actual LEDs or cathodes of the screen. When this ACPI option is available, the illumination is controllable using a GUI slider in the Display/Screen system settings or by simple commands on the CLI.
Different cards might manage this differently. Check /sys/class/backlight to find out:
# ls /sys/class/backlight/intel_backlight
The directory contains the following files and folders:
actual_brightness brightness max_brightness subsystem/ uevent
# cat /sys/class/backlight/acpi_video0/max_brightness
# echo 5 > /sys/class/backlight/acpi_video0/brightness
acpi_osi=Linux acpi_backlight=vendor
acpi_osi=Linux acpi_backlight=legacy
看了这个之后，很显然，问题就在于acpi_backlight=vendor will prefer vendor specific driver (e.g. thinkpad_acpi, sony_acpi, etc.) instead of the ACPI video.ko driver.
本文来源：博客园 作者：浮沉雄鹰