[hal-info] Dell laptops control brightness in hardware

Rui Tiago Matos tiagomatos at gmail.com
Wed Nov 14 18:11:08 CST 2007

[cross posting to a dell list so that the relevant people can provide
more insight]

On 14/11/2007, Martin Pitt <martin at piware.de> wrote:
> hi Rui,


> Rui Tiago Matos [2007-11-14 19:37 +0000]:
> > Besides, doesn't the existence of the dell backlight addon make it
> > software controlled?
> You can't, it's hardwired (as Danny pointed out already). AFAIUI, the
> file you pointed out just tells hal that it uses the Dell specific
> backend for brightness control, which I guess will just read out the
> new brightness without actually trying to set it. (I might be wrong
> here, I don't know much about the Dell perculiarity).

Well, I have a Latitude D630 running Fedora 8 and currently this is
how it works:

1. the dcdbas module has got to be loaded before hal starts so that
the dell addon is loaded by hal. I've put it in the initrd (ugly hack
but it works. Matt Domsch had done the right fix for it, see [1]).

2. gnome power manager is able to change the brightness on software
using said dell addon which uses dell's libsmbios. The libsmbios CLI
tools can also set the brightness (i.e. dellLcdBrightness).

3. what doesn't work right (see [2]) is notification from the hardware
(or BIOS?) --> hal when one uses the keys.

Furthermore I think people at Dell are aware of these problems[3].


[1] https://bugzilla.redhat.com/show_bug.cgi?id=248257

[2] https://bugzilla.redhat.com/show_bug.cgi?id=356091 - search for my
description of what happens on Fn+Up/Down

[3] http://lists.freedesktop.org/archives/dbus/2007-May/007668.html

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