trident XP4m32 brightness change

René Rebe rene at
Sun Jul 22 09:42:01 PDT 2007


On Sunday 22 July 2007 20:33:08 Mathieu Lacage wrote:
> On Sun, 2007-07-22 at 18:02 +0200, René Rebe wrote:
> > > 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.
> Actually, I might have been wrong: using the /proc/acpi/... brightness
> control seems to trigger the acpi video code (I tried both the
> toshiba-specific acpi video extensions and the normal acpi video
> support) located in drivers/acpi/video.c or drivers/acpi/toshiba_acpi.c,
> both of which involve triggering the acpi interpreter. Is this what you
> meant when you said that "the bios is doing the ... register tinkering
> in this case" ?


> > 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.
> The current trident driver seems to contain already code to control the
> brightness. I suspect that this code is controlled by the
> "GammaBrightness" config file option which is not super useful to me.

Gamma is not brightness. it is the non-linear mapping of color values.

Based on the initial mail I thought you want to change your display
backlight in order to save power?

> xbacklight seems to require randr 1.2 support which is not in my current
> server. I suspect that this would require adding full xrandr 1.2 support
> to the trident driver, right ? Or could I manage to just put enough
> support to make this work ?

You do not need to implement the BACKLIGHT atom, for an example see:



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