debugging backlight issues

[Kamal Mostafa]

Hi David-

On Mon, 2010-06-14 at 18:36 -0400, David Tombs wrote:

> 2) I have a laptop where the brightness hotkeys work, but there's
> nothing in /sys/backlight and /proc/acpi/video/*/backlight reads "<not
> supported>". Do some laptops have the keys directly connected to the
> hardware or something?

I imagine that's possible...  On that laptop, do you see the GUI
"brightness notification popup"?  If you do then the software must be
involved somehow; if you don't then maybe the keys are indeed directly
wired to the hardware.


> 3) Is there any way to "blacklist" ACPI control of the backlight if it
> doesn't work? This would be for laptops where acpi=off fixes the
> brightness keys but the user naturally doesn't want to use this all the
> time.

I think the param "acpi.brightness_switch_enabled=0" does what you're
looking for.

Also note:  I've written an experimental patch which lets Intel
i915-driver GPU's take over backlight brightness control from ACPI (for
situations where the ACPI method is broken).  It is currently pending
review upstream but you're welcome to try it if you wish.  See:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/568611
(comment #20 points to my latest test kernel)

 -Kamal
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part
URL: <https://lists.ubuntu.com/archives/kernel-team/attachments/20100616/a2016b1a/attachment.sig>