trident XP4m32 brightness change

Mathieu Lacage Mathieu.Lacage at
Sun Jul 22 11:33:08 PDT 2007

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.

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 ?


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