--- linux-4.14.33/drivers/gpu/drm/i915/intel_bios.c.orig	2017-11-12 19:46:13.000000000 +0100
+++ linux-4.14.33/drivers/gpu/drm/i915/intel_bios.c	2018-04-11 02:51:36.150529907 +0200
@@ -1206,12 +1206,24 @@
 			info->alternate_ddc_pin = 0;
 		}
 
+		if (!intel_gmbus_is_valid_pin(dev_priv, info->alternate_ddc_pin)) {
+			DRM_ERROR("pin %d is invalid for port %c, ignore it\n",
+				info->alternate_ddc_pin, port_name(port));
+			info->alternate_ddc_pin = 0;
+		}
+
 		sanitize_ddc_pin(dev_priv, port);
 	}
 
 	if (is_dp) {
 		info->alternate_aux_channel = aux_channel;
 
+		if (!intel_gmbus_is_valid_pin(dev_priv, aux_channel)) {
+			DRM_ERROR("pin %d is invalid for port %c, ignore it\n",
+				aux_channel, port_name(port));
+			info->alternate_aux_channel = 0;
+		}
+
 		sanitize_aux_ch(dev_priv, port);
 	}