trident XP4m32 brightness change

René Rebe rene at
Sun Jul 22 09:02:26 PDT 2007

On Sunday 22 July 2007 15:39:05 Mathieu Lacage wrote:
> hi,
> If, under X, I try to change the brightness of my laptop's lcd panel
> with the following command:
> echo "brightness: 1" > /proc/acpi/toshiba/lcd
> the screen resolution changes abruptly: it switches from 1024x768 (the
> panel's native resolution) to what I believe is 320x.... forcing a VT
> switch back and forth brings back the old resolution with the new
> brightness. 
> Is there something which can be done to make the trident driver
> synchronize with the kernel-level brightness change ? Or is just a bug
> in my linux vesafb driver (which, I suspect, is responsible for
> performing the brightness change once it is requested through acpi).

The BIOS is doing the brightness change register tinkering in this case,
and apparently touched some surrounding registers as well.

Maybe try to figure out what register is used for the brightness control
and add support the "backlight change via xrandr" (also see xbacklight)
to have full control about the behaviour.


  René Rebe - ExactCODE GmbH - Europe, Germany, Berlin
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