Comment 124 for bug 333386

If you prefer, here is attached

2009/10/9 Stefan Bader <email address hidden>

> Please attach the ouput of dmesg (while using one of the two ways of
> specifying
> the options) and attach it here.
>
> --
> Acer: Cannot change brightness with 2.6.27-11+ kernel
> https://bugs.launchpad.net/bugs/333386
> You received this bug notification because you are a direct subscriber
> of a duplicate bug.
>
> Status in “linux” package in Ubuntu: Fix Released
> Status in linux in Ubuntu Intrepid: Fix Released
> Status in linux in Ubuntu Jaunty: Fix Released
> Status in linux in Ubuntu Karmic: Fix Released
>
> Bug description:
> SRU justification:
>
> Impact: After I carelessly pulled in some updates to the ACPI video code,
> we were faced with some regressions. One was (at least) a certain Acer
> laptop model that suddenly had no backlight control.
>
> Fix: As the ACPI BIOS is broken on a way that only the *wrong* graphics
> definition will be accepted by acpi-video as the right definition lacks an
> attribute to be considered, the fix is to have less strict requirements to
> that check, so the definition for the right graphics device gets accepted (a
> patch doing that unconditionally, has been submitted upstream and has been
> acked, but might not make it until 2.6.32). For the stable tree I created
> more code which makes sure the less strict tests only take effect on that
> laptop or when the user really wants to.
>
> Testcase: Booting on another laptop will not activate the code (which
> prints a "Using less strict video detection..." message) but will do with
> "acpi_video_strict_detect=0". In both cases nothing bad happened. The
> affected laptop boots and selects the new check which gives back the
> backlight control.
>
> ---
>
> Since the 2.6.27-11 generic kernel (also in 2.6.27-12) I cannot change the
> backlight brightness anymore. In the latest kernel, it seems there's no more
> file in /proc/acpi/video, but GFX0 still apears in 2.6.27-9 where I can
> still change brightness. I'm new to linux so if you need information give me
> the command to run. It's an acer 6920G laptop.
>