So going through the kernel log at
https://launchpad.net/ubuntu/+source/linux/
This appears to broke in 2.6.24-11.17 with one of the following entries that
was pulled from upstream:
* ACPI: video: Rationalise ACPI backlight implementation <-- "This is most
likely the culprit"
* ACPI: video: Ignore ACPI video devices that aren't present in hardware
This is currently broken in 2.6.25 (which I assume where these patches
were pulled from).
Now remember it "works" with 2.6.25-10.16.
So what we know:
- This effects only Thinkpads with Intel x3100
- This broke with 2.6.24-11.17 update
- There is a really bad work around using thinkpad acpi ...
please read <kernel source>/Documentation/thinkpa-acpi.txt
It says and I quote .. " When display backlight brightness controls
are available
through the standard ACPI interface, it is best to use it instead of
this direct
ThinkPad-specific interface."
* So you should not be using backlight= thinkpad_acpi option
* The problem is the ACPI interface is broken, so please stop
mentioning it in this bug
- Also even though you see the Gnome backlight indicator slowly going up
and down, the actual backlight is not changing.
--
[REGRESSION] Impossible to change LCD brightness on Thinkpad R61/T61/X61
https://bugs.launchpad.net/bugs/198476
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