SRU update for acpi backlight problems

[Stefan Bader]

Stefan Bader wrote:
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/311716
> 
> SRU justification:
> 
> Impact: Some laptops had issues with the current backlight control. This 
> is because up to then acpi and vendor specific control methods were 
> able/allowed to access the video hardware 
> (https://bugs.launchpad.net/bugs/257827). The fix for this (taken from 
> upstream) fixes this but causes regressions for others. So for stable it 
> should probably be taken back but this would cause an ABI bump.
> 
> Fix: I changed the detection code in a (slightly ugly to keep diff 
> minimal) way to make the old behaviour the default (generic _and_ vendor 
> control at the same time) but leave the infrastructure (no ABI bump) 
> which gives the additional ability for those that have problems with 
> that to force either generic (video) or vendor specific (vendor) by 
> using the module option acpi_backlight.
> 
> Testcase: Boot the kernel and try to adjust backlight levels with 
> FN-keys and/or the gnome backlight applet.
> 
> Note: going over the original acpi patches, it looks like some vendor 
> drivers might have been fixed wrong (eg. sony-laptop.c which bails out 
> on !acpi_backlight_suppoert(). But that is the case when acpi is _not_ 
> active).
> 

One addition to that: the T61 seems to be odd off. There is a change to fix 
acpi from poking on the wrong video device. But then thinkpad_acpi detects this 
is thee and backs of. Unfortunately generic support does not work as expected.
Probably because T61 in one of the rare machines that have _OSI=Linux enabled, 
so the ACPI bios can act differently there...


-- 

When all other means of communication fail, try words!


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