[drm] 3.18 regression: backlight dark after resume

["Ortwin Glück" <odi@odi.ch>]

Hi,

Since 3.18-rc1 backlight is dark after resume from suspend. This is on a Samsung 
laptop with i5 IvyBridge

00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor 
Graphics Controller (rev 09)


I have bisected this problem to the following commit:
73580fb764c4213d305c0d36bd8f856ae631eb42 is the first bad commit
commit 73580fb764c4213d305c0d36bd8f856ae631eb42
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Tue Aug 12 17:11:41 2014 +0300

     drm/i915/dp: make backlight bl_power control power sequencer backlight

     This lets the userspace switch off the backlight using the backlight
     class sysfs bl_power file. The switch is done using the power sequencer;
     the backlight PWM, and everything else, remains enabled. The display
     backlight won't draw power, but for maximum power savings the encoder
     needs to be switched off.

     Signed-off-by: Jani Nikula <jani.nikula@intel.com>
     Reviewed_by: Clinton Taylor <Clinton.A.Taylor@intel.com>
     Tested_by: Clinton Taylor <Clinton.A.Taylor@intel.com>
     Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>


Thanks,

Ortwin