drm/i915: Handle downstream facing ports w/o EDID

Use drm_dp_downstream_mode() to get a suitable mode for downstream
facing ports which don't have an EDID.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904115354.25336-15-ville.syrjala@linux.intel.comReviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/display/intel_dp.c

@@ -6313,7 +6313,7 @@ static int intel_dp_get_modes(struct drm_connector *connector)
 	}
 
 	/* if eDP has no EDID, fall back to fixed mode */
-	if (intel_dp_is_edp(intel_attached_dp(to_intel_connector(connector))) &&
+	if (intel_dp_is_edp(intel_attached_dp(intel_connector)) &&
 	    intel_connector->panel.fixed_mode) {
 		struct drm_display_mode *mode;
 
@@ -6325,6 +6325,19 @@ static int intel_dp_get_modes(struct drm_connector *connector)
 		}
 	}
 
+	if (!edid) {
+		struct intel_dp *intel_dp = intel_attached_dp(intel_connector);
+		struct drm_display_mode *mode;
+
+		mode = drm_dp_downstream_mode(connector->dev,
+					      intel_dp->dpcd,
+					      intel_dp->downstream_ports);
+		if (mode) {
+			drm_mode_probed_add(connector, mode);
+			return 1;
+		}
+	}
+
 	return 0;
 }