drm/i915/edp: Do not do link training fallback or prune modes on EDP

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>

1 files changed, 17 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 05907fa8a553..cf8fef8b6f58 100644
--- 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_dp *intel_dp)
 	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;
 }