[Bug 47941] [snb] Backlight control broken between 3.6.0-rc1 and 3.6.0-rc4

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=47941





--- Comment #69 from Kamal Mostafa <kamal at canonical.com>  2013-04-08 21:41:17 ---
Created an attachment (id=97751)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=97751)
drm/i915: quirk no PCH_PWM_ENABLE for Dell XPS13 backlight

The commit "cf0a658 drm/i915: write backlight harder" enabled mostly* working
brightness control for the Dell XPS 13 (both Sandy Bridge and Ivy Bridge).  But
since that has now been reverted (b128937) those machines are back to
non-functional brightness control again.

The attached patch provides a DMI quirk fix which fixes brightness controls for
the Dell XPS 13 family, slightly better* than "write backlight harder".

Feedback is invited: Does this fix your XPS 13 brightness control?

*The "write backlight harder" fix stops working after screensaver idle-out per
https://bugs.launchpad.net/bugs/1162026 ; this fix continues working.

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