From 2059ac3b1304cb6a82f9d90762dea9f556831627 Mon Sep 17 00:00:00 2001
From: Jani Nikula <jani.nikula@intel.com>
Date: Fri, 26 Jun 2015 14:18:56 +0300
Subject: [PATCH] drm/i915: fix backlight after resume on 855gm
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Some 855gm models (at least ThinkPad X40) regressed because of

commit b0cd324faed23d10d66ba6ade66579c681feef6f
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Wed Nov 12 16:25:43 2014 +0200

    drm/i915: don't save/restore backlight hist ctl registers

which tried to make our driver more robust by not blindly saving and
restoring registers, but it failed to take into account

commit 0eb96d6ed38430b72897adde58f5477a6b71757a
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Wed Oct 14 12:33:41 2009 -0700

    drm/i915: save/restore BLC histogram control reg across suspend/resume

Fix the regression by enabling hist ctl on gen2.

v2: Improved the comment.

v3: Improved the comment, again.

Reported-and-tested-by: Philipp Gesang <phg@phi-gamma.net>
References: http://mid.gmane.org/20150623222648.GD12335@acheron
Fixes: b0cd324faed2 ("drm/i915: don't save/restore backlight hist ctl registers")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
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