usbnet: introduce usbnet_link_change API

This patch introduces the API of usbnet_link_change, so that
usbnet can handle link change centrally, which may help to
implement killing traffic URBs for saving USB bus bandwidth
and host controller power.
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/usbnet.c

@@ -1653,6 +1653,19 @@ int usbnet_manage_power(struct usbnet *dev, int on)
 }
 EXPORT_SYMBOL(usbnet_manage_power);
 
+void usbnet_link_change(struct usbnet *dev, bool link, bool need_reset)
+{
+	/* update link after link is reseted */
+	if (link && !need_reset)
+		netif_carrier_on(dev->net);
+	else
+		netif_carrier_off(dev->net);
+
+	if (need_reset && link)
+		usbnet_defer_kevent(dev, EVENT_LINK_RESET);
+}
+EXPORT_SYMBOL(usbnet_link_change);
+
 /*-------------------------------------------------------------------------*/
 static int __usbnet_read_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
 			     u16 value, u16 index, void *data, u16 size)

include/linux/usb/usbnet.h

@@ -245,5 +245,6 @@ extern void usbnet_get_drvinfo(struct net_device *, struct ethtool_drvinfo *);
 extern int usbnet_nway_reset(struct net_device *net);
 
 extern int usbnet_manage_power(struct usbnet *, int);
+extern void usbnet_link_change(struct usbnet *, bool, bool);
 
 #endif /* __LINUX_USB_USBNET_H */