diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
index 3250c1b8dcca..36f1425652c1 100644
--- a/drivers/gpu/drm/i915/display/intel_bios.c
+++ b/drivers/gpu/drm/i915/display/intel_bios.c
@@ -2114,16 +2114,22 @@ static bool child_dev_is_dp_dual_mode(const struct child_device_config *child,
 		[PORT_F] = { DVO_PORT_DPF, DVO_PORT_HDMIF, },
 	};
 
+	DRM_DEBUG_KMS("%s: port=%d\n", __func__, port);
 	if (port == PORT_A || port >= ARRAY_SIZE(port_mapping))
 		return false;
 
+	DRM_DEBUG_KMS("%s: 0x%x & 0x%x, 0x%x & 0x%x\n",
+		      __func__, child->device_type, DEVICE_TYPE_DP_DUAL_MODE_BITS, DEVICE_TYPE_DP_DUAL_MODE, DEVICE_TYPE_DP_DUAL_MODE_BITS);
 	if ((child->device_type & DEVICE_TYPE_DP_DUAL_MODE_BITS) !=
 	    (DEVICE_TYPE_DP_DUAL_MODE & DEVICE_TYPE_DP_DUAL_MODE_BITS))
 		return false;
 
+	DRM_DEBUG_KMS("%s: child->dvo_port=%u, port_mapping[port].dp=%u\n", __func__, child->dvo_port, port_mapping[port].dp);
 	if (child->dvo_port == port_mapping[port].dp)
 		return true;
 
+	DRM_DEBUG_KMS("%s: child->dvo_port=%u, port_mapping[port].hdmi=%u, child->aux_channel=%u\n",
+		      __func__, child->dvo_port, port_mapping[port].hdmi, child->aux_channel);
 	/* Only accept a HDMI dvo_port as DP++ if it has an AUX channel */
 	if (child->dvo_port == port_mapping[port].hdmi &&
 	    child->aux_channel != 0)
@@ -2141,6 +2147,7 @@ bool intel_bios_is_port_dp_dual_mode(struct drm_i915_private *dev_priv,
 	for (i = 0; i < dev_priv->vbt.child_dev_num; i++) {
 		child = dev_priv->vbt.child_dev + i;
 
+		DRM_DEBUG_KMS("%s: checking %d/%d\n", __func__, i, dev_priv->vbt.child_dev_num);
 		if (child_dev_is_dp_dual_mode(child, port))
 			return true;
 	}
diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index e02f0faecf02..013ad3b68cc8 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -2471,10 +2471,14 @@ intel_hdmi_dp_dual_mode_detect(struct drm_connector *connector, bool has_edid)
 	 * confusing log messages about DP dual mode adaptors when
 	 * there's nothing connected to the port.
 	 */
+	DRM_DEBUG_KMS("%s: original type %d\n", __func__, type);
 	if (type == DRM_DP_DUAL_MODE_UNKNOWN) {
 		/* An overridden EDID imply that we want this port for testing.
 		 * Make sure not to set limits for that port.
 		 */
+		DRM_DEBUG_KMS("%s: has_edid=%s, !connector->override_edid=%s, intel_bios_is_port_dp_dual_mode returns %s\n",
+			      __func__, has_edid ? "true":"false", !connector->override_edid ? "true":"false",
+			      intel_bios_is_port_dp_dual_mode(dev_priv, port) ? "true":"false");
 		if (has_edid && !connector->override_edid &&
 		    intel_bios_is_port_dp_dual_mode(dev_priv, port)) {
 			DRM_DEBUG_KMS("Assuming DP dual mode adaptor presence based on VBT\n");
@@ -2484,6 +2488,7 @@ intel_hdmi_dp_dual_mode_detect(struct drm_connector *connector, bool has_edid)
 		}
 	}
 
+	DRM_DEBUG_KMS("%s: final type %d\n", __func__, type);
 	if (type == DRM_DP_DUAL_MODE_NONE)
 		return;