[hal-info] Dell laptops control brightness in hardware

[Michael E Brown]

On Thu, Nov 15, 2007 at 12:11:08AM +0000, Rui Tiago Matos wrote:
> [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,
> 
> Hi!
> 
> > 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.

The brightness control keys produce a key scancode which can be mapped
to tell HAL what is going on. I havent looked into this myself. I think
ubuntu does something like this, as I saw a similar inquiry a few days
ago on ubunutu.
--
Michael