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[Attilio <nexor@xxxxxxxx>]

Hi everyone, I have an Acer 4810TG which is affected by this bug. I have 3 OSs installed: Windows 7 64bit, Ubuntu 10.4 32bit and Fedora 13 64bit (KDE only), and the bios version is 1.35 (released April 22nd).
The new bios didn't make any difference for me, otherwise here is what i could observe:
-on W7, the brightness hotkeys do work, but not very accurately: i can apparently set 10 different levels, but the lower three have the same brightness, so that the last 2 keypresses when decreasing, and 2 when increasing it cause no effect at all; furthermore i have no OSD feedback. These glitches could be sign of poor support to W7 from Acer, I had Vista preinstalled.
- On Ubuntu with the given workaround (nomodeset apci_backlight=vendor) the controls work very well, ~20 levels with the nice OSD. Unfortunately this cannot be done in F13, which requires KMS on intel cards.
- On Ubuntu and Fedora with desktop effects disabled, and default kernel arguments (except "i8042.nomux", needed for a touchpad bug), thus with KMS enabled, i have a behavior similar to W7, but with even more inaccurate control: the number of levels is not fixed, and i get an OSD which, at least on Fedora, shows incorrect values. What's more interesting is that as soon as i reactivate compositing everything freezes. In Ubuntu the only way to recover control is to forcibly shut down the notebook, whilst in fedora i can restart the X server (with ctrl+alt+back) but only start new sessions without compositing, if i login to a user having it enabled i get stuck at the loading splashscreen.
An interesting fact is that ANY OPENGL ACTIVITY seems to trigger the bug, not only enabling desktop compositing but also starting "glxgears" for example causes me a system freeze, although not always immediately.

I think this bug is not in compiz, but in kernel modesetting instead!
Unluckily I currently don't have the time to do much further testing,
such as some with the Radeon discrete GPU (i got some freezes with that
to, anyway).

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[gm45] Adjusting Brightness in Acer Aspire Timelines causes system freeze in 4810T and 5810T models
https://bugs.launchpad.net/bugs/446717
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