usb: Create link files between child device and usb port device.

To show the relationship between usb port and child device,
add link file "port" under usb device's sysfs directoy and
"device" under usb port device's sysfs directory. They are linked
to each other.
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NLan Tianyu <tianyu.lan@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hub.c

@@ -1989,6 +1989,14 @@ void usb_disconnect(struct usb_device **pdev)
 	usb_disable_device(udev, 0);
 	usb_hcd_synchronize_unlinks(udev);
 
+	if (udev->parent) {
+		struct usb_port	*port_dev =
+			hdev_to_hub(udev->parent)->ports[udev->portnum - 1];
+
+		sysfs_remove_link(&udev->dev.kobj, "port");
+		sysfs_remove_link(&port_dev->dev.kobj, "device");
+	}
+
 	usb_remove_ep_devs(&udev->ep0);
 	usb_unlock_device(udev);
 
@@ -2281,6 +2289,24 @@ int usb_new_device(struct usb_device *udev)
 		goto fail;
 	}
 
+	/* Create link files between child device and usb port device. */
+	if (udev->parent) {
+		struct usb_port *port_dev =
+			hdev_to_hub(udev->parent)->ports[udev->portnum - 1];
+
+		err = sysfs_create_link(&udev->dev.kobj,
+				&port_dev->dev.kobj, "port");
+		if (err)
+			goto fail;
+
+		err = sysfs_create_link(&port_dev->dev.kobj,
+				&udev->dev.kobj, "device");
+		if (err) {
+			sysfs_remove_link(&udev->dev.kobj, "port");
+			goto fail;
+		}
+	}
+
 	(void) usb_create_ep_devs(&udev->dev, &udev->ep0, udev);
 	usb_mark_last_busy(udev);
 	pm_runtime_put_sync_autosuspend(&udev->dev);