usbnet: mcs7830: rework link state detection

Even with the quirks in commit dabdaf0c (mcs7830: Fix link state
detection) there are still spurious link-down events for some chips
where the false link-down events count go over a few hundreds.

This patch takes a more conservative approach and only looks at
link-down events where the link-down state is not combined with other
states (e.g. half/full speed, pending frames in SRAM or TX status
information valid). In all other cases we assume the link is up.

Tested on MCS7830CV-DA (USB ID 9710:7830).

Cc: Ondrej Zary <linux@rainbow-software.org>
Cc: Michael Leun <lkml20120218@newton.leun.net>
Cc: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/mcs7830.c

@@ -117,7 +117,6 @@ enum {
 struct mcs7830_data {
 	u8 multi_filter[8];
 	u8 config;
-	u8 link_counter;
 };
 
 static const char driver_name[] = "MOSCHIP usb-ethernet driver";
@@ -561,26 +560,16 @@ static void mcs7830_status(struct usbnet *dev, struct urb *urb)
 {
 	u8 *buf = urb->transfer_buffer;
 	bool link, link_changed;
-	struct mcs7830_data *data = mcs7830_get_data(dev);
 
 	if (urb->actual_length < 16)
 		return;
 
-	link = !(buf[1] & 0x20);
+	link = !(buf[1] == 0x20);
 	link_changed = netif_carrier_ok(dev->net) != link;
 	if (link_changed) {
-		data->link_counter++;
-		/*
-		   track link state 20 times to guard against erroneous
-		   link state changes reported sometimes by the chip
-		 */
-		if (data->link_counter > 20) {
-			data->link_counter = 0;
 		usbnet_link_change(dev, link, 0);
 		netdev_dbg(dev->net, "Link Status is: %d\n", link);
 	}
-	} else
-		data->link_counter = 0;
 }
 
 static const struct driver_info moschip_info = {