Naive question on brightness keys

[Hans-Werner Hilse]

Hi,

On Wed, 29 Aug 2007 10:08:58 -0400 (EDT) Radu-Cristian FOTESCU
<beranger5ca at yahoo.ca> wrote:

> Why is DragonFly's kernel (and some other kernels) "eating" my
> brightness adjustment keys with my Acer?

Because those aren't handled by any software. Nothing is eaten. But
nothing is provided either.

> 1. The said keys _can_ interact *directly with the hardware* ? as
> proven by the fact that they work while you're in the BIOS screen (or
> at the GRUB/LILO prompt, or before the kernel is fully loaded), and
> they also work sometimes when the kernel is still detecting hardware
> and couldn't be aware yet of any model-specific hardware. 

No, this is a misconception. When something works in real mode it is
not meaning that it is a purely hardware-based functionality. After
all, most complex functionality is *not* purely hardware-based. In this
case, the BIOS probably provides *software* hooks which only work in
real mode. In most cases, the software hooks are still accessible in
APM mode (as opposed to ACPI). So running without ACPI and using APM
would be a first step.

> 2.  With or without the interaction of the said keys, a very few Linux
> distros are able to adjust my screen brightness in increments of 1%,
> from 0 to 100, through software ? e.g. KPowerSave: "Your hardware
> supports to change the brightness". While I appreciate the fact that
> this can be achieved through software (yet I don't know what can
> XF86BrightnessAdjust be set to trigger, exactly!?), I still want to
> be able to adjust the brightness manually (the 9 levels I can get
> through the keyboard) ? simply because unlike the volume keys, it's
> very rare to have software able to adjust the screen brightness. 

There's software for setting brightness (e.g. ddccontrol, I'm not sure
what software would fit your model). And there's software for binding
stuff to keys. Combined, following the basic UNIX principles, you can
get your keyboard-driven brightness control. Some of this software can
make the needed calls itself, using known interfaces. There's e.g.
khotkeys, hotkeys, ...

> You can see a cross-OS synopsis here:
> http://beranger.org/blogo3/brightness_keys.png

and the harsh, though not very informed text can be found here:
http://beranger.org/index.php?page=diary&2007/08/27/08/28/31-frivolous-monday


-hwh