mcs7830: Implement link state detection

Add .status callback that detects link state changes.
Tested with MCS7832CV-AA chip (9710:7830, identified as rev.C by the driver).
Fixes https://bugzilla.kernel.org/show_bug.cgi?id=28532

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/mcs7830.c

@@ -629,11 +629,31 @@ static int mcs7830_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 	return skb->len > 0;
 }
 
+static void mcs7830_status(struct usbnet *dev, struct urb *urb)
+{
+	u8 *buf = urb->transfer_buffer;
+	bool link;
+
+	if (urb->actual_length < 16)
+		return;
+
+	link = !(buf[1] & 0x20);
+	if (netif_carrier_ok(dev->net) != link) {
+		if (link) {
+			netif_carrier_on(dev->net);
+			usbnet_defer_kevent(dev, EVENT_LINK_RESET);
+		} else
+			netif_carrier_off(dev->net);
+		netdev_dbg(dev->net, "Link Status is: %d\n", link);
+	}
+}
+
 static const struct driver_info moschip_info = {
 	.description	= "MOSCHIP 7830/7832/7730 usb-NET adapter",
 	.bind		= mcs7830_bind,
 	.rx_fixup	= mcs7830_rx_fixup,
-	.flags		= FLAG_ETHER,
+	.flags		= FLAG_ETHER | FLAG_LINK_INTR,
+	.status		= mcs7830_status,
 	.in		= 1,
 	.out		= 2,
 };
@@ -642,7 +662,8 @@ static const struct driver_info sitecom_info = {
 	.description    = "Sitecom LN-30 usb-NET adapter",
 	.bind		= mcs7830_bind,
 	.rx_fixup	= mcs7830_rx_fixup,
-	.flags		= FLAG_ETHER,
+	.flags		= FLAG_ETHER | FLAG_LINK_INTR,
+	.status		= mcs7830_status,
 	.in		= 1,
 	.out		= 2,
 };