releases/4.0.4/drm-i915-assume-dual-channel-lvds-if-pixel-clock-necessitates-it.patch

From 6f317cfe42c9d8a7c9c1a327d2f1bcc517a3cd91 Mon Sep 17 00:00:00 2001
From: Lukas Wunner <lukas@wunner.de>
Date: Sun, 12 Apr 2015 21:10:35 +0200
Subject: drm/i915: Assume dual channel LVDS if pixel clock necessitates it
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From: Lukas Wunner <lukas@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 <lukas@wunner.de>
Tested-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[Jani: included spec reference into the commit message]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/i915/intel_lvds.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -847,6 +847,11 @@ static bool compute_is_dual_link_lvds(st
 	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;
 
@@ -1104,6 +1109,8 @@ void intel_lvds_init(struct drm_device *
 out:
 	mutex_unlock(&dev->mode_config.mutex);
 
+	intel_panel_init(&intel_connector->panel, fixed_mode, downclock_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");
@@ -1118,7 +1125,6 @@ out:
 	}
 	drm_connector_register(connector);
 
-	intel_panel_init(&intel_connector->panel, fixed_mode, downclock_mode);
 	intel_panel_setup_backlight(connector, INVALID_PIPE);
 
 	return;