[Jaunty] SRU: Fix video backlight regression on Acer laptop

Stefan Bader stefan.bader at canonical.com
Thu Aug 27 22:09:49 UTC 2009

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.


When all other means of communication fail, try words!

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