[Bug 415023] Re: brightness is broken on MSI WIND U100

[Guido Berhoerster]

Please read comment 37, comment 65 and comment 69. The problem has been
completely triaged, the MSI Wind handles brightness through the BIOS BUT
each change of brightness levels also emits a keypress event which is
then handled by gnome-power-manager, powerdevil, or xfce4-power-manager.
There are two different problems:

The first issue with this is that each keypress changes brightness
twice, resulting effectively in only 4 instead of 8 levels that the
hardware is capable of. This is happens with all previous releases of
Ubuntu as well.

The second issue is new in 9.10 and has been intoduced with kernel
modesetting, that is gnome-power-manager and equivalents start switching
back and forth between two adjacent brightness levels either due to a
rounding bug or feedback loop (remeber that each time brightness levels
are changed in software keypresses are emitted as well).

There is actually a workaround for the second issue (the flickering
people report over and over) and that is disabling kernel modesetting by
passing nomodeset to the kernel at boot time.

The solution to this problem is that power management software needs to
be told that the brightness keys are handled in hardware. In the past
this could be done by setting the HAL property
laptop_panel.brightness_in_hardware to true as Felix Geyer has pointed
out, however this is not read by gnome-power-manager because it handles
the backlight through xrandr instead of HAL.

-- 
brightness is broken on MSI WIND U100
https://bugs.launchpad.net/bugs/415023
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