j613: second external display with the lid closed (internal pipe on the left-front port)

arch/arm64/boot/dts/apple/t8122-j613.dts

@@ -651,14 +651,61 @@
 	};
 };
 
+/*
+ * With the lid closed the internal DCP's pipe can drive a second external
+ * display on the left-front port. In the J613 ADT the
+ * internal DCP is display-crossbar ufp0, port 0, which is crossbar state 0
+ * (dispext0,0) on ATC1's crossbar, DPTX target 1 like dcpext's route@1. The
+ * pipe's first DPTX core drives the panel otherwise, so the display driver
+ * only offers this route while the lid is closed and the panel is off, and
+ * only to a display that dcpext cannot take.
+ *
+ * The route stays disabled here, like dcpext's: the display gate enables it
+ * together with dcpext. The front connector has one endpoint per pipeline
+ * that can drive it, as on the M1 Pro/Max laptops.
+ */
+&dcp {
+	phys = <&atcphy1 PHY_TYPE_DP>;
+	phy-names = "typec0";
+	mux-controls = <&atcphy1_xbar 0>;
+	mux-control-names = "typec0";
+	apple,typec-mux-indices = <0>;
+	apple,typec-dptx-phys = <1>;
+
+	typec-routes {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		route@0 {
+			reg = <0>;
+			mode-switch;
+			status = "disabled";
+
+			port {
+				dcp_typec1: endpoint {
+					remote-endpoint = <&typec1_dcp>;
+				};
+			};
+		};
+	};
+};
+
 &typec1 {
 	ports {
 		port@3 {
 			reg = <3>;
+			#address-cells = <1>;
+			#size-cells = <0>;
 
-			typec1_dcpext: endpoint {
+			typec1_dcpext: endpoint@0 {
+				reg = <0>;
 				remote-endpoint = <&dcpext_typec1>;
 			};
+
+			typec1_dcp: endpoint@1 {
+				reg = <1>;
+				remote-endpoint = <&dcp_typec1>;
+			};
 		};
 	};
 };

drivers/gpu/drm/apple/Kconfig

@@ -15,6 +15,7 @@ config DRM_APPLE
 	select DRM_GEM_DMA_HELPER
 	select VIDEOMODE_HELPERS
 	depends on BACKLIGHT_CLASS_DEVICE
+	depends on INPUT
 	select MULTIPLEXER
 	select DRM_APPLE_FABRIC_CORE
 	help

drivers/gpu/drm/apple/apple_drv.c

@@ -222,8 +222,10 @@ apple_connector_detect(struct drm_connector *connector, bool force)
 		return connector_status_connected;
 	if (connector->force == DRM_FORCE_OFF)
 		return connector_status_disconnected;
-	return dcp_connector_connected(apple_connector) ?
-		connector_status_connected : connector_status_disconnected;
+	if (!dcp_connector_connected(apple_connector) ||
+	    dcp_clamshell_hold_connector(apple_connector))
+		return connector_status_disconnected;
+	return connector_status_connected;
 }
 
 static void apple_connector_oob_hotplug(struct drm_connector *connector,