usb: assign default peer ports for root hubs

Assume that the peer of a superspeed port is the port with the same id
on the shared_hcd root hub. This identification scheme is required of
external hubs by the USB3 spec [1]. However, for root hubs, tier mismatch
may be in effect [2]. Tier mismatch can only be enumerated via platform
firmware. For now, simply perform the nominal association.

A new lock 'usb_port_peer_mutex' is introduced to synchronize port
device add/remove with peer lookups. It protects peering against
changes to hcd->shared_hcd, hcd->self.root_hub, hdev->maxchild, and
port_dev->child pointers.

[1]: usb 3.1 section 10.3.3
[2]: xhci 1.1 appendix D

Cc: Alan Stern <[e-mail]>
[alan: usb_port_peer_mutex locking scheme]
Acked-by: Alan Stern <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/hcd.c

···
 		mutex_init(hcd->bandwidth_mutex);
 		dev_set_drvdata(dev, hcd);
 	} else {
+		mutex_lock(&usb_port_peer_mutex);
 		hcd->bandwidth_mutex = primary_hcd->bandwidth_mutex;
 		hcd->primary_hcd = primary_hcd;
 		primary_hcd->primary_hcd = primary_hcd;
 		hcd->shared_hcd = primary_hcd;
 		primary_hcd->shared_hcd = hcd;
+		mutex_unlock(&usb_port_peer_mutex);
 	}
 
 	kref_init(&hcd->kref);
···
  * deallocated.
  *
  * Make sure to only deallocate the bandwidth_mutex when the primary HCD is
- * freed.  When hcd_release() is called for the non-primary HCD, set the
- * primary_hcd's shared_hcd pointer to null (since the non-primary HCD will be
- * freed shortly).
+ * freed.  When hcd_release() is called for either hcd in a peer set
+ * invalidate the peer's ->shared_hcd and ->primary_hcd pointers to
+ * block new peering attempts
  */
-static void hcd_release (struct kref *kref)
+static void hcd_release(struct kref *kref)
 {
 	struct usb_hcd *hcd = container_of (kref, struct usb_hcd, kref);
 
+	mutex_lock(&usb_port_peer_mutex);
 	if (usb_hcd_is_primary_hcd(hcd))
 		kfree(hcd->bandwidth_mutex);
-	else
-		hcd->shared_hcd->shared_hcd = NULL;
+	if (hcd->shared_hcd) {
+		struct usb_hcd *peer = hcd->shared_hcd;
+
+		peer->shared_hcd = NULL;
+		if (peer->primary_hcd == hcd)
+			peer->primary_hcd = NULL;
+	}
+	mutex_unlock(&usb_port_peer_mutex);
 	kfree(hcd);
 }
 
···
 	return 0;
 }
 
+/*
+ * Before we free this root hub, flush in-flight peering attempts
+ * and disable peer lookups
+ */
+static void usb_put_invalidate_rhdev(struct usb_hcd *hcd)
+{
+	struct usb_device *rhdev;
+
+	mutex_lock(&usb_port_peer_mutex);
+	rhdev = hcd->self.root_hub;
+	hcd->self.root_hub = NULL;
+	mutex_unlock(&usb_port_peer_mutex);
+	usb_put_dev(rhdev);
+}
+
 /**
  * usb_add_hcd - finish generic HCD structure initialization and register
  * @hcd: the usb_hcd structure to initialize
···
 		retval = -ENOMEM;
 		goto err_allocate_root_hub;
 	}
+	mutex_lock(&usb_port_peer_mutex);
 	hcd->self.root_hub = rhdev;
+	mutex_unlock(&usb_port_peer_mutex);
 
 	switch (hcd->speed) {
 	case HCD_USB11:
···
 err_request_irq:
 err_hcd_driver_setup:
 err_set_rh_speed:
-	usb_put_dev(hcd->self.root_hub);
+	usb_put_invalidate_rhdev(hcd);
 err_allocate_root_hub:
 	usb_deregister_bus(&hcd->self);
 err_register_bus:
···
 			free_irq(hcd->irq, hcd);
 	}
 
-	usb_put_dev(hcd->self.root_hub);
 	usb_deregister_bus(&hcd->self);
 	hcd_buffer_destroy(hcd);
 	if (hcd->remove_phy && hcd->phy) {
···
 		usb_put_phy(hcd->phy);
 		hcd->phy = NULL;
 	}
+
+	usb_put_invalidate_rhdev(hcd);
 }
 EXPORT_SYMBOL_GPL(usb_remove_hcd);
 

drivers/usb/core/hub.c

···
 
 static struct task_struct *khubd_task;
 
+/* synchronize hub-port add/remove and peering operations */
+DEFINE_MUTEX(usb_port_peer_mutex);
+
 /* cycle leds on hubs that aren't blinking for attention */
 static bool blinkenlights = 0;
 module_param (blinkenlights, bool, S_IRUGO);
···
 	char *message = "out of memory";
 	unsigned unit_load;
 	unsigned full_load;
+	unsigned maxchild;
 
 	hub->buffer = kmalloc(sizeof(*hub->buffer), GFP_KERNEL);
 	if (!hub->buffer) {
···
 		goto fail;
 	}
 
-	hdev->maxchild = hub->descriptor->bNbrPorts;
-	dev_info (hub_dev, "%d port%s detected\n", hdev->maxchild,
-		(hdev->maxchild == 1) ? "" : "s");
+	maxchild = hub->descriptor->bNbrPorts;
+	dev_info(hub_dev, "%d port%s detected\n", maxchild,
+			(maxchild == 1) ? "" : "s");
 
-	hub->ports = kzalloc(hdev->maxchild * sizeof(struct usb_port *),
-			     GFP_KERNEL);
+	hub->ports = kzalloc(maxchild * sizeof(struct usb_port *), GFP_KERNEL);
 	if (!hub->ports) {
 		ret = -ENOMEM;
 		goto fail;
···
 		int	i;
 		char	portstr[USB_MAXCHILDREN + 1];
 
-		for (i = 0; i < hdev->maxchild; i++)
+		for (i = 0; i < maxchild; i++)
 			portstr[i] = hub->descriptor->u.hs.DeviceRemovable
 				    [((i + 1) / 8)] & (1 << ((i + 1) % 8))
 				? 'F' : 'R';
-		portstr[hdev->maxchild] = 0;
+		portstr[maxchild] = 0;
 		dev_dbg(hub_dev, "compound device; port removable status: %s\n", portstr);
 	} else
 		dev_dbg(hub_dev, "standalone hub\n");
···
 		if (hcd->power_budget > 0)
 			hdev->bus_mA = hcd->power_budget;
 		else
-			hdev->bus_mA = full_load * hdev->maxchild;
+			hdev->bus_mA = full_load * maxchild;
 		if (hdev->bus_mA >= full_load)
 			hub->mA_per_port = full_load;
 		else {
···
 			hub->descriptor->bHubContrCurrent);
 		hub->limited_power = 1;
 
-		if (remaining < hdev->maxchild * unit_load)
+		if (remaining < maxchild * unit_load)
 			dev_warn(hub_dev,
 					"insufficient power available "
 					"to use all downstream ports\n");
···
 	if (hub->has_indicators && blinkenlights)
 		hub->indicator[0] = INDICATOR_CYCLE;
 
-	for (i = 0; i < hdev->maxchild; i++) {
+	mutex_lock(&usb_port_peer_mutex);
+	for (i = 0; i < maxchild; i++) {
 		ret = usb_hub_create_port_device(hub, i + 1);
 		if (ret < 0) {
 			dev_err(hub->intfdev,
 				"couldn't create port%d device.\n", i + 1);
-			hdev->maxchild = i;
-			goto fail_keep_maxchild;
+			break;
 		}
 	}
+	hdev->maxchild = i;
+	mutex_unlock(&usb_port_peer_mutex);
+	if (ret < 0)
+		goto fail;
 
 	usb_hub_adjust_deviceremovable(hdev, hub->descriptor);
 
···
 	return 0;
 
 fail:
-	hdev->maxchild = 0;
-fail_keep_maxchild:
 	dev_err (hub_dev, "config failed, %s (err %d)\n",
 			message, ret);
 	/* hub_disconnect() frees urb and descriptor */
···
 	hub->error = 0;
 	hub_quiesce(hub, HUB_DISCONNECT);
 
+	mutex_lock(&usb_port_peer_mutex);
+
 	/* Avoid races with recursively_mark_NOTATTACHED() */
 	spin_lock_irq(&device_state_lock);
 	port1 = hdev->maxchild;
···
 
 	for (; port1 > 0; --port1)
 		usb_hub_remove_port_device(hub, port1);
+
+	mutex_unlock(&usb_port_peer_mutex);
 
 	if (hub->hdev->speed == USB_SPEED_HIGH)
 		highspeed_hubs--;
···
 		 */
 		status = 0;
 
+		mutex_lock(&usb_port_peer_mutex);
+
 		/* We mustn't add new devices if the parent hub has
 		 * been disconnected; we would race with the
 		 * recursively_mark_NOTATTACHED() routine.
···
 		else
 			port_dev->child = udev;
 		spin_unlock_irq(&device_state_lock);
+		mutex_unlock(&usb_port_peer_mutex);
 
 		/* Run it through the hoops (find a driver, etc) */
 		if (!status) {
 			status = usb_new_device(udev);
 			if (status) {
+				mutex_lock(&usb_port_peer_mutex);
 				spin_lock_irq(&device_state_lock);
 				port_dev->child = NULL;
 				spin_unlock_irq(&device_state_lock);
+				mutex_unlock(&usb_port_peer_mutex);
 			}
 		}
 

drivers/usb/core/hub.h

···
  * @child: usb device attached to the port
  * @dev: generic device interface
  * @port_owner: port's owner
+ * @peer: related usb2 and usb3 ports (share the same connector)
  * @connect_type: port's connect type
  * @portnum: port index num based one
  * @power_is_on: port's power state
···
 	struct usb_device *child;
 	struct device dev;
 	struct usb_dev_state *port_owner;
+	struct usb_port *peer;
 	enum usb_port_connect_type connect_type;
 	u8 portnum;
 	unsigned power_is_on:1;

drivers/usb/core/port.c

···
 	.owner = THIS_MODULE,
 };
 
+static void link_peers(struct usb_port *left, struct usb_port *right)
+{
+	if (left->peer == right && right->peer == left)
+		return;
+
+	if (left->peer || right->peer) {
+		struct usb_port *lpeer = left->peer;
+		struct usb_port *rpeer = right->peer;
+
+		WARN(1, "failed to peer %s and %s (%s -> %p) (%s -> %p)\n",
+			dev_name(&left->dev), dev_name(&right->dev),
+			dev_name(&left->dev), lpeer,
+			dev_name(&right->dev), rpeer);
+		return;
+	}
+
+	left->peer = right;
+	right->peer = left;
+}
+
+static void unlink_peers(struct usb_port *left, struct usb_port *right)
+{
+	WARN(right->peer != left || left->peer != right,
+			"%s and %s are not peers?\n",
+			dev_name(&left->dev), dev_name(&right->dev));
+
+	right->peer = NULL;
+	left->peer = NULL;
+}
+
+/* set the default peer port for root hubs */
+static void find_and_link_peer(struct usb_hub *hub, int port1)
+{
+	struct usb_port *port_dev = hub->ports[port1 - 1], *peer;
+	struct usb_device *hdev = hub->hdev;
+
+	if (!hdev->parent) {
+		struct usb_hub *peer_hub;
+		struct usb_device *peer_hdev;
+		struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
+		struct usb_hcd *peer_hcd = hcd->shared_hcd;
+
+		if (!peer_hcd)
+			return;
+
+		peer_hdev = peer_hcd->self.root_hub;
+		peer_hub = usb_hub_to_struct_hub(peer_hdev);
+		if (!peer_hub || port1 > peer_hdev->maxchild)
+			return;
+
+		peer = peer_hub->ports[port1 - 1];
+
+		if (peer)
+			link_peers(port_dev, peer);
+	}
+}
+
 int usb_hub_create_port_device(struct usb_hub *hub, int port1)
 {
-	struct usb_port *port_dev = NULL;
+	struct usb_port *port_dev;
 	int retval;
 
 	port_dev = kzalloc(sizeof(*port_dev), GFP_KERNEL);
···
 	retval = device_register(&port_dev->dev);
 	if (retval)
 		goto error_register;
+
+	find_and_link_peer(hub, port1);
 
 	pm_runtime_set_active(&port_dev->dev);
 
···
 	return retval;
 }
 
-void usb_hub_remove_port_device(struct usb_hub *hub,
-				       int port1)
+void usb_hub_remove_port_device(struct usb_hub *hub, int port1)
 {
-	device_unregister(&hub->ports[port1 - 1]->dev);
-}
+	struct usb_port *port_dev = hub->ports[port1 - 1];
+	struct usb_port *peer;
 
+	peer = port_dev->peer;
+	if (peer)
+		unlink_peers(port_dev, peer);
+	device_unregister(&port_dev->dev);
+}

drivers/usb/core/usb.h

···
 #endif
 
 extern struct bus_type usb_bus_type;
+extern struct mutex usb_port_peer_mutex;
 extern struct device_type usb_device_type;
 extern struct device_type usb_if_device_type;
 extern struct device_type usb_ep_device_type;