Naive question on brightness keys

[Radu-Cristian FOTESCU]

Since the DragonFly users are likely to be mostly its developers, I am asking
this question here. (Tirez pas sur le pianiste.)

--- start of exposé --

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

To the extent of my lack of knowledge, the problem with adjusting the screen
brightness is that it seems to have two parts, regardless of the OS:

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. 

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. 

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

So FreeBSD and NetBSD seem to "leave those key alone" so they can adjust the
brightness, whereas DragonFly BSD is interfering with them!

--- end of exposé --

Question: How does it happen? How can a keycode *not* be "sensed" in the same
hardware that can "sense" it in the bootloader screen? What is DragonFly
doing?

Thank you.
R-C



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