From: Felipe Contreras <felipe.contreras@gmail.com>
Date: Sat, 3 Aug 2013 21:00:25 +0000 (+0200)
Subject: ACPI / video: improve quirk check in acpi_video_bqc_quirk()
X-Git-Tag: v3.11-rc5~11^2~1^2~4
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b3b301c5fed8a0868e56c98b922cb0c881b3857d;p=pandora-kernel.git

ACPI / video: improve quirk check in acpi_video_bqc_quirk()

If the _BCL package ordering is descending, the first level
(br->levels[2]) is likely to be 0, and if the number of levels
matches the number of steps, we might confuse a returned level to
mean the index.

For example:

  current_level = max_level = 100
  test_level = 0
  returned level = 100

In this case 100 means the level, not the index, and _BCM failed.
Still, if the _BCL package ordering is descending, the index of
level 0 is also 100, so we assume _BQC is indexed, when it's not.

This causes all _BQC calls to return bogus values causing weird
behavior from the user's perspective.  For example:

xbacklight -set 10; xbacklight -set 20;

would flash to 90% and then slowly down to the desired level (20).

The solution is simple; test anything other than the first level
(e.g. 1).

[rjw: Changelog]
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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