Also of possible interest. On my system I have three devices of class "backlight":
> ls -l /sys/class/backlight/ total 0 lrwxrwxrwx 1 root root 0 Jun 12 14:17 acpi_video0 -> ../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0 lrwxrwxrwx 1 root root 0 Jun 12 13:39 acpi_video1 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video1 lrwxrwxrwx 1 root root 0 Jun 12 14:17 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight Each of these devices has a file inside called "brightness". The way these files change is interesting and suggests there is a probelem/confusion/interaction among acpi_video0 and acpi_video1 I could see what happens with the following command: watch -d -n 0.1 "cat /sys/class/backlight/acpi_video0/brightness && cat /sys/class/backlight/acpi_video1/brightness && cat /sys/class/backlight/intel_backlight/brightness" then watching how the values change in reaction to brightness keypresses. The intel_backlight/brightness value stands fixed at 497 The acpi_video0/brightness and acpi_video1/brightness values are normally not the same. e.g. the following happens: Values are: 6 -- 7 then I do one Fn+ArrowUP keypress for increasing brighness. After 1s, values become (but brightness does not change): 8 -- 7 Then after 1s and at 0.5s intervals, they change to 8 -- 9 8 -- 10 8 -- 11 One thing it always happens is that after a single keypress of brightness up (down), the first value acpi_video0/brightness gets the value of acpi_video1/brightness plus (minus) one, respectively. Then acpi_video1/brightness continues to change in the same direction. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/847001 Title: Adjusting display brightness is very slow on several Dell laptops To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-power-manager/+bug/847001/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
