Since Linux kernel v3.18-rc1, it contains
commit e6755fb78e8f20ecadf2a4080084121336624ad9 Author: Jani Nikula <jani.nikula at intel.com> Date: Tue Aug 12 17:11:42 2014 +0300
drm/i915: switch off backlight for backlight class 0 brightness
Since Linux kernel v3.18-rc1, it contains
commit e6755fb78e8f20e cadf2a408008412 1336624ad9
Author: Jani Nikula <jani.nikula at intel.com>
Date: Tue Aug 12 17:11:42 2014 +0300
drm/i915: switch off backlight for backlight class 0 brightness