[DellStudioXPS1340] Brightness Fn keys do not work properly

[Julian Lam]

Binary package hint: acpi

The brightness keys seem to work fine on a cold start - but after hibernating or suspending, or even switching from AC to battery, the brightness keys don't work properly.

Intended effect:
Brightness-Up and -Down keys increment monitor brightness by equal amounts (to a maximum of 15)

Actual effect:
Brightness is incremented by seemingly random amounts, and on occasion, brightness will randomly jump to an arbitrary value.

Notes:
Writing to /sys/devices/virtual/backlight/acpi_video0/brightness works fine. Just the hotkeys are malfunctioning.

ProblemType: Bug
Architecture: amd64
Date: Thu Feb 18 22:06:33 2010
DistroRelease: Ubuntu 9.10
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
NonfreeKernelModules: wl nvidia
Package: acpi (not installed)
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-19.56-generic
SourcePackage: acpi
Uname: Linux 2.6.31-19-generic x86_64

[Julian Lam (julian-lam)]

More testing has yielded this find:

It seems as though the laptop brightness works like my old Dell 700m. Plug in the power cable, the brightness immediately increases (to the preset value), unplug it, it immediately dims, with no transition between brightness states.

With the XPS 1340, whenever brightness settings are changed, the brightness values change immediately (i.e. from 7 to 15) with no transition, but Ubuntu (or acpi) resets it back down and incrementally increases it from 7 to 15. Ditto for brightness decreases.

So it seems like acpi can't decide whether or not it should incrementally change the brightness, or just set it once and forget it.

Hopefully, I can provide logs, if someone can tell me where to look!