I have a Clevo P751DM-G with a GeForce GTX 980M, running Ubuntu 16.04 and nvidia 367.27.
Issue: when setting laptop’s LCD brightness up and down with the Fn-F8/Fn-F9 keys, this has no effect on the LCD screen.
After some investigations, I found that the Fn-keys are properly generating ACPI events:
$ acpi_listen video/brightnessdown BRTDN 00000087 00000000 video/brightnessup BRTUP 00000086 00000000
The video module provides /sys/class/backlight/acpi_video0.
Pressing Fn-keys properly increase/decrease the value in /sys/class/backlight/acpi_video0/brightness, but writing into it has no effect on the screen (but the new value is still saved).
Also, the Desktop Environment open a popup indicating a change in brightness setting.
=> Everything seems to be working on the ACPI event side.
On the other hand, I can change brightness with
xbacklight -set XX or
nvidia-settings -n -a BacklightBrightness=XX.
=> This has real effect on the screen.
So, the only missing piece seems to be the glue between ACPI events and brightness control.
I know I can workaround it with an acpid event handler, but I expect it to work out of the box without any manual script hacking.
- Is my expectation correct?
- What can I do to further investigate the issue? (are there some logs to look for? should I provide some more information?)
- Is this an nvidia driver issue or should I look for other component? (Xorg, kernel, …)