drm/apple, tipd: keep DP-alt ports without a display off the Type-C pipelines

drivers/gpu/drm/apple/dcp-fabric.c

@@ -1378,6 +1378,45 @@ static int dcp_typec_port_busy(struct apple_dcp_typec_port *port,
 	return -ENOSPC;
 }
 
+/*
+ * PD controllers report a DP state at probe for ports with no display behind
+ * them, an empty port or one with a dock that has none, and whichever port is
+ * routed first wins the pipeline.  A port whose sink asserts HPD and finds no
+ * free pipeline takes one over from a direct DP-alt port whose sink never
+ * did.  Tunnels, ports in a SAFE transition and pipelines whose fixed output
+ * is in use are left alone.  The released port drops its applied state, so
+ * its next update is routed again once a pipeline is free.
+ */
+static struct apple_dcp_typec_route *
+dcp_typec_take_over_without_hpd(struct apple_dcp_typec_port *port)
+{
+	struct apple_dcp_typec_route *candidate;
+
+	list_for_each_entry(candidate, &port->routes, port_link) {
+		struct apple_dcp_typec_route *held =
+			candidate->dcp->active_typec_route;
+		int ret;
+
+		if (!held || held->tunnel || held->port == port ||
+		    held->port->hpd || held->port->dp_hpd ||
+		    held->port->safe_pending ||
+		    dcp_typec_route_busy(candidate))
+			continue;
+
+		ret = dcp_typec_route_deactivate(held);
+		if (ret)
+			return ERR_PTR(ret);
+		held->port->owner = NULL;
+		held->port->applied_valid = false;
+		dev_info(candidate->dcp->dev,
+			 "released Type-C DPTX PHY %u held without HPD\n",
+			 held->dptx_phy);
+		return candidate;
+	}
+
+	return NULL;
+}
+
 static int dcp_typec_route_set(struct typec_mux_dev *mux,
 			       struct typec_mux_state *state)
 {
@@ -1518,10 +1557,27 @@ static int dcp_typec_route_set(struct typec_mux_dev *mux,
 	}
 
 	if (!port->owner) {
+		/*
+		 * Nothing behind the port asserts HPD yet, a dock without a
+		 * display for one: leave the pipelines to ports with a display.
+		 * The port controller reports HPD as a new status when a sink
+		 * appears, and the port is routed then.  A port that already
+		 * owns a pipeline keeps it across an HPD drop, as before.
+		 */
+		if (!hpd) {
+			port->hpd = false;
+			port->applied_valid = true;
+			return 0;
+		}
+
 		best = dcp_typec_free_route(port);
+		if (!best)
+			best = dcp_typec_take_over_without_hpd(port);
+		if (IS_ERR(best))
+			return PTR_ERR(best);
 		/* Every pipeline is driving another port's display. */
 		if (!best)
-			return hpd ? dcp_typec_port_busy(port, route->dcp) : -ENOSPC;
+			return dcp_typec_port_busy(port, route->dcp);
 
 		ret = dcp_typec_route_activate(best, best->xbar);
 		if (ret)

drivers/usb/typec/tipd/cd321x-pm-test.c

@@ -713,7 +713,7 @@ static void cd321x_display_taken_test(struct kunit *test)
 	KUNIT_EXPECT_FALSE(test, cd321x_display_taken(0, true));
 	/* Other SoCs keep -EBUSY as the taken display. */
 	KUNIT_EXPECT_TRUE(test, cd321x_display_taken(-EBUSY, false));
-	KUNIT_EXPECT_FALSE(test, cd321x_display_taken(-ENOSPC, false));
+	KUNIT_EXPECT_TRUE(test, cd321x_display_taken(-ENOSPC, false));
 	KUNIT_EXPECT_FALSE(test, cd321x_display_taken(-EAGAIN, false));
 	KUNIT_EXPECT_FALSE(test, cd321x_display_taken(0, false));
 }

drivers/usb/typec/tipd/cd321x-pm.h

@@ -355,12 +355,14 @@ static inline void cd321x_pm_remove(struct cd321x_pm_state *pm)
 /*
  * A display mux reports -ENOSPC when every display pipeline is driving
  * another port.  That lasts until the other display goes away, so the port's
- * USB path is set up without the display and nothing is retried.  Any other
- * error, such as -EBUSY from a PHY in the middle of a transition, is retried.
+ * USB path is set up without the display and nothing is retried.  The DCP
+ * fabric reports it as -ENOSPC on every SoC now; older trees used -EBUSY
+ * outside H17, which is still accepted there.  Any other error, such as
+ * -EBUSY from an H17 PHY in the middle of a transition, is retried.
  */
 static inline bool cd321x_display_taken(int ret, bool enospc)
 {
-	return ret == (enospc ? -ENOSPC : -EBUSY);
+	return ret == -ENOSPC || (!enospc && ret == -EBUSY);
 }
 
 enum cd321x_dp_send {