xfce4-power-manager doesn't detect brightness controls on T440s backlight control is actually supported by xrandr and xbacklight works correctly. Problem is caused by display name: ~ » xrandr Screen 0: minimum 320 x 200, current 1600 x 900, maximum 8192 x 8192 eDP1 connected 1600x900+0+0 (normal left inverted right x axis y axis) 309mm x 174mm 1600x900 60.0*+ 1024x768 60.0 800x600 60.3 56.2 640x480 59.9 DP1 disconnected (normal left inverted right x axis y axis) HDMI1 disconnected (normal left inverted right x axis y axis) DP2 disconnected (normal left inverted right x axis y axis) HDMI2 disconnected (normal left inverted right x axis y axis) at the same time in xfpm-brightness.c, xfpm_brightness_setup_xrandr expects display name to start with "LVDS". Commenting this check out fixes the problem.
Since I also use the T440s, I have added support for the intel backlight. If you could try current git, you will notice the backlight controls will work better now. A remaining bug is control via the keyboard brightness up/down keys; it seems xfce power manager interferes with the intel driver here. Try to lower brightness to 0 or push it to its maximum, then continue hitting the brightness down / up key. The level will suddenly jump up from zero / down from maximum. Can you confirm this misbehaviour?
I've found out what was wrong on my system: The ACPI video driver registers its own backlight driver (/sys/class/backlight/acpi_video0/) and wires up the brightness up/down keys and this way interferes with everything else. Adding video.use_native_backlight=1 to the kernel command line gets rid of it, and xfce4-power-manager works correctly. Of course, the backlight keys stop working on the kernel console, but I can live with that.
(In reply to Harald Judt from comment #2) > I've found out what was wrong on my system: The ACPI video driver registers > its own backlight driver (/sys/class/backlight/acpi_video0/) and wires up > the brightness up/down keys and this way interferes with everything else. > Adding video.use_native_backlight=1 to the kernel command line gets rid of > it, and xfce4-power-manager works correctly. Of course, the backlight keys > stop working on the kernel console, but I can live with that. Right, I wonder if we can resolve this in some way, there are currently several brightness-related bugs: https://bugzilla.xfce.org/show_bug.cgi?id=7541 https://bugzilla.xfce.org/show_bug.cgi?id=8248 https://bugzilla.xfce.org/show_bug.cgi?id=10456
Much easier than to deactivate the ACPI video module on the command line is to disable the /sys/module/video/parameters/brightness_switch_enabled.
@Harald: Hasn't this issue been fixed already in the 1.3.1 release?
Yes, and it definitely works on my system ;-)
Alright, marking as fixed then.