From a306343bcd7df89d9d45a601929e26866e7b7a81 Mon Sep 17 00:00:00 2001
From: Manasi Navare <manasi.d.navare@intel.com>
Date: Thu, 12 Oct 2017 12:13:38 -0700
Subject: [PATCH] drm/i915/edp: Do not do link training fallback or prune modes on EDP
Git-commit: a306343bcd7df89d9d45a601929e26866e7b7a81
Patch-mainline: v4.16-rc1
References: FATE#322643 bsc#1055900
No-fix: c0cfb10d9e1de490e36d3b9d4228c0ea0ca30677

In case of eDP because the panel has a fixed mode, the link rate
and lane count at which it is trained corresponds to the link BW
required to support the native resolution of the panel. In case of
panles with lower resolutions where fewer lanes are hooked up internally,
that number is reflected in the MAX_LANE_COUNT DPCD register of the panel.
So it is pointless to fallback to lower link rate/lane count in case
of link training failure on eDP connector since the lower link BW
will not support the native resolution of the panel and we cannot
prune the preferred mode on the eDP connector.

In case of Link training failure on the eDP panel, something is wrong
in the HW internally and hence driver errors out with a loud
and clear DRM_ERROR message.

V2: 
* Fix the DEBUG_ERROR and add {} in else (Ville Syrjala)

Cc: Clinton Taylor <clinton.a.taylor@intel.com>
Cc: Jim Bride <jim.bride@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Reference: https://bugs.freedesktop.org/show_bug.cgi?id=103369
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1507835618-23051-1-git-send-email-manasi.d.navare@intel.com
(cherry picked from commit c0cfb10d9e1de490e36d3b9d4228c0ea0ca30677)

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/intel_dp_link_training.c |   26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -328,14 +328,22 @@ intel_dp_start_link_train(struct intel_d
 	return;
 
  failure_handling:
-	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
-		      intel_connector->base.base.id,
-		      intel_connector->base.name,
-		      intel_dp->link_rate, intel_dp->lane_count);
-	if (!intel_dp_get_link_train_fallback_values(intel_dp,
-						     intel_dp->link_rate,
-						     intel_dp->lane_count))
-		/* Schedule a Hotplug Uevent to userspace to start modeset */
-		schedule_work(&intel_connector->modeset_retry_work);
+	/* Dont fallback and prune modes if its eDP */
+	if (!intel_dp_is_edp(intel_dp)) {
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
+			      intel_connector->base.base.id,
+			      intel_connector->base.name,
+			      intel_dp->link_rate, intel_dp->lane_count);
+		if (!intel_dp_get_link_train_fallback_values(intel_dp,
+							     intel_dp->link_rate,
+							     intel_dp->lane_count))
+			/* Schedule a Hotplug Uevent to userspace to start modeset */
+			schedule_work(&intel_connector->modeset_retry_work);
+	} else {
+		DRM_ERROR("[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
+			  intel_connector->base.base.id,
+			  intel_connector->base.name,
+			  intel_dp->link_rate, intel_dp->lane_count);
+	}
 	return;
 }