[ltp] Command to dim the LCD brightness

[André Wyrwa]

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Hi Bob,

> t40:/proc/acpi/video/VID/LCD0# cat brightness
> <not supported>

yepp, same here.

> Last question: I cannot find why in Debian other ACPI modules are=20
> automatically loaded but video was not ... ideas ?

Not a debianiac ;-), but i guess it's because this module is new in
2.6.10 and so Debian doen't know about it.

There should be some file /etc/sysconfig/modules or something like that
listing modules that are going to be loaded at startup. If you put a
line for the video module in there it should be included at boot time.

> ACPI: Video Device [VID] (multi-head: yes  rom: no  post: no)

This probably means...ACPI display switching is possible, mutli-head is
possible, no video rom found, no POST data found (don't really know
anything about that). I guess that brightness is not supported because
the rom is not found.

> Unable to handle kernel NULL pointer dereference at virtual address 00000=
004
>   printing eip:
> f8b388b1
> *pde =3D 00000000
> Oops: 0000 [#1]

Ooops, what's that? Might come from echoing 0
into /proc/acpi/video/LCD0/brightness. Guess you shouldn't do it as long
as it's not supported.

As the kernel docu says, it's a reference implementation, meaning that
it resembles the specifications as they are defined by ACPI. As usual
hardware sticks too this less tight as we might wish, and it seems that
this is the case in our ThinkPads. So we can just hope that this driver
improves.

BTW: On my machine the LCD brightness is lowered through some BIOS
setting automatically when i unplug AC. Maybe not all the way, but a bit
at least. Even though i use ACPI.

Andr=E9.


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