thunderbolt: Improve redrive mode handling

When USB-C monitor is connected directly to Intel Barlow Ridge host, it
goes into "redrive" mode that basically routes the DisplayPort signals
directly from the GPU to the USB-C monitor without any tunneling needed.
However, the host router must be powered on for this to work. Aaron
reported that there are a couple of cases where this will not work with
the current code:

- Booting with USB-C monitor plugged in.
- Plugging in USB-C monitor when the host router is in sleep state
(runtime suspended).
- Plugging in USB-C device while the system is in system sleep state.

In all these cases once the host router is runtime suspended the picture
on the connected USB-C display disappears too. This is certainly not
what the user expected.

For this reason improve the redrive mode handling to keep the host
router from runtime suspending when detect that any of the above cases
is happening.

Fixes: a75e0684efe5 ("thunderbolt: Keep the domain powered when USB4 port is in redrive mode")
Reported-by: Aaron Rainbolt <[e-mail]>
Closes: https://lore.kernel.org/linux-usb/20241009220118.70bfedd0@kf-ir16/
Cc: [e-mail]
Signed-off-by: Mika Westerberg <[e-mail]>

drivers/thunderbolt/tb.c

···
 	}
 }
 
+static void tb_switch_enter_redrive(struct tb_switch *sw)
+{
+	struct tb_port *port;
+
+	tb_switch_for_each_port(sw, port)
+		tb_enter_redrive(port);
+}
+
+/*
+ * Called during system and runtime suspend to forcefully exit redrive
+ * mode without querying whether the resource is available.
+ */
+static void tb_switch_exit_redrive(struct tb_switch *sw)
+{
+	struct tb_port *port;
+
+	if (!(sw->quirks & QUIRK_KEEP_POWER_IN_DP_REDRIVE))
+		return;
+
+	tb_switch_for_each_port(sw, port) {
+		if (!tb_port_is_dpin(port))
+			continue;
+
+		if (port->redrive) {
+			port->redrive = false;
+			pm_runtime_put(&sw->dev);
+			tb_port_dbg(port, "exit redrive mode\n");
+		}
+	}
+}
+
 static void tb_dp_resource_unavailable(struct tb *tb, struct tb_port *port)
 {
 	struct tb_port *in, *out;
···
 	tb_create_usb3_tunnels(tb->root_switch);
 	/* Add DP IN resources for the root switch */
 	tb_add_dp_resources(tb->root_switch);
+	tb_switch_enter_redrive(tb->root_switch);
 	/* Make the discovered switches available to the userspace */
 	device_for_each_child(&tb->root_switch->dev, NULL,
 			      tb_scan_finalize_switch);
···
 
 	tb_dbg(tb, "suspending...\n");
 	tb_disconnect_and_release_dp(tb);
+	tb_switch_exit_redrive(tb->root_switch);
 	tb_switch_suspend(tb->root_switch, false);
 	tcm->hotplug_active = false; /* signal tb_handle_hotplug to quit */
 	tb_dbg(tb, "suspend finished\n");
···
 		tb_dbg(tb, "tunnels restarted, sleeping for 100ms\n");
 		msleep(100);
 	}
+	tb_switch_enter_redrive(tb->root_switch);
 	 /* Allow tb_handle_hotplug to progress events */
 	tcm->hotplug_active = true;
 	tb_dbg(tb, "resume finished\n");
···
 	struct tb_cm *tcm = tb_priv(tb);
 
 	mutex_lock(&tb->lock);
+	/*
+	 * The below call only releases DP resources to allow exiting and
+	 * re-entering redrive mode.
+	 */
+	tb_disconnect_and_release_dp(tb);
+	tb_switch_exit_redrive(tb->root_switch);
 	tb_switch_suspend(tb->root_switch, true);
 	tcm->hotplug_active = false;
 	mutex_unlock(&tb->lock);
···
 	tb_restore_children(tb->root_switch);
 	list_for_each_entry_safe(tunnel, n, &tcm->tunnel_list, list)
 		tb_tunnel_restart(tunnel);
+	tb_switch_enter_redrive(tb->root_switch);
 	tcm->hotplug_active = true;
 	mutex_unlock(&tb->lock);