Peter Clifton pcjc2 at cam.ac.uk
Tue Nov 20 15:54:53 PST 2007

On Tue, 2007-11-20 at 23:05 +0000, Colin Guthrie wrote:
> Sergio Monteiro Basto wrote:
> > On Tue, 2007-11-20 at 21:39 +0100, Lukas Hejtmanek wrote:
> >> Hello,
> >>
> >> I noticed that you did some improvements to the backlight support in the video
> >> driver. Would it be possible to add an option "do not touch backlight"?
> >>
> >> Currently, I use backlight level 0 and I highly dislike that starting the
> >> X server or playing a movie in mplayer rises backlight to level 7. I do not
> >> want it.
> >>
> > 
> > backlight support, is the lid button ?
> No backlight is the light behind the lcd. It /should/ (arguable) be
> turned off when the lid is closed (as there is little point it in being
> on!!), but this is probably something that should be controlled by
> something higher up the stack than the driver (please correct me if I'm
> wrong). I say this more out of principle rather than practicality as I
> cannot think of *any* reason why the backlight should remain on with the
> lid closed (and thus there is nothing wrong with this being in the
> driver), but the whole backlight control (dim level) when on power vs
> battery and what to do when the lid is closed (suspend, nowt, depend on
> power status etc.) are probably all handled by the same system e.g.
> gnome-power-manager or equiv (again please correct me if I'm wrong here
> and this is a pure HAL thing....)

AFAIK, the Xorg driver asks the BIOS not to do the backlight turn on /
off with the lid switch, so the BIOS doesn't change brightness registers
behind the driver's back.

The driver should ensure some safety measure is in place to switch the
back-light off when the lid is shut, as not doing so results in
overheated laptops.

Best wishes,

Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,

Tel: +44 (0)7729 980173 - (No signal in the lab!)

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