drm/i915: write backlight harder
770c1231 is the first bad commit commit 770c1231 Author: Takashi Iwai <tiwai@suse.de> Date: Sat Aug 11 08:56:42 2012 +0200 drm/i915: Fix blank panel at reopening lid changed the register write sequence for restoring the backlight, which helped prevent non-working backlights on some machines. Turns out that the original sequence was the right thing to do for a different set of machines. Worse, setting the backlight level _after_ enabling it seems to reset it somehow. So we need to make that one conditional upon the backlight having been reset to zero, and add the old one back. Cargo-culting at it's best, but it seems to work. Cc: stable@vger.kernel.org Cc: Takashi Iwai <tiwai@suse.de> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=47941Reviewed-by: Jani Nikula <jani.nikula@intel.com> Acked-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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