3.13.11-ckt22 -stable review patch.  If anyone has any objections, please let 
me know.

------------------

From: Lukas Wunner <lu...@wunner.de>

commit 6f317cfe42c9d8a7c9c1a327d2f1bcc517a3cd91 upstream.

Single channel LVDS maxes out at 112 MHz, anything above must be dual
channel. This avoids the need to specify i915.lvds_channel_mode=2 on
all 17" MacBook Pro models with i915 graphics since they had 1920x1200
(193 MHz), plus those 15" pre-retina models which had a resolution
of 1680x1050 (119 MHz) as a BTO option.

Source for 112 MHz limit of single channel LVDS is section 2.3 of:
https://01.org/linuxgraphics/sites/default/files/documentation/ivb_ihd_os_vol3_part4.pdf

v2: Avoid hardcoding 17" models by assuming dual channel LVDS if the
resolution necessitates it, suggested by Jani Nikula.

v3: Fix typo, thanks Joonas Lahtinen.

v4: Split commit in two, suggested by Ville Syrjälä.

Signed-off-by: Lukas Wunner <lu...@wunner.de>
Tested-by: Lukas Wunner <lu...@wunner.de>
Reviewed-by: Ville Syrjälä <ville.syrj...@linux.intel.com>
[Jani: included spec reference into the commit message]
Signed-off-by: Jani Nikula <jani.nik...@intel.com>
[ kamal: backport to 3.13-stable ]
Signed-off-by: Kamal Mostafa <ka...@canonical.com>
---
 drivers/gpu/drm/i915/intel_lvds.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_lvds.c 
b/drivers/gpu/drm/i915/intel_lvds.c
index a837510..0f3a188 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -891,6 +891,11 @@ static bool compute_is_dual_link_lvds(struct 
intel_lvds_encoder *lvds_encoder)
        if (i915_lvds_channel_mode > 0)
                return i915_lvds_channel_mode == 2;
 
+       /* single channel LVDS is limited to 112 MHz */
+       if (lvds_encoder->attached_connector->base.panel.fixed_mode->clock
+           > 112999)
+               return true;
+
        if (dmi_check_system(intel_dual_link_lvds))
                return true;
 
@@ -1131,6 +1136,8 @@ void intel_lvds_init(struct drm_device *dev)
                goto failed;
 
 out:
+       intel_panel_init(&intel_connector->panel, fixed_mode);
+
        lvds_encoder->is_dual_link = compute_is_dual_link_lvds(lvds_encoder);
        DRM_DEBUG_KMS("detected %s-link lvds configuration\n",
                      lvds_encoder->is_dual_link ? "dual" : "single");
@@ -1142,7 +1149,6 @@ out:
        }
        drm_sysfs_connector_add(connector);
 
-       intel_panel_init(&intel_connector->panel, fixed_mode);
        intel_panel_setup_backlight(connector);
 
        return;
-- 
1.9.1

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