mcs7830: Fix link state detection

The device had an undocumented "feature": it can provide a sequence of
spurious link-down status data even if the link is up all the time.
A sequence of 10 was seen so update the link state only after the device
reports the same link state 20 times.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Reported-by: Michael Leun <lkml20120218@newton.leun.net>
Tested-by: Michael Leun <lkml20120218@newton.leun.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 21 insertions, 9 deletions

diff --git a/drivers/net/usb/mcs7830.c b/drivers/net/usb/mcs7830.c
index 03c2d8d653df..cc7e72010ac3 100644
--- a/drivers/net/usb/mcs7830.c
+++ b/drivers/net/usb/mcs7830.c
@@ -117,6 +117,7 @@ enum {
 struct mcs7830_data {
         u8 multi_filter[8];
         u8 config;
+        u8 link_counter;
 };
 
 static const char driver_name[] = "MOSCHIP usb-ethernet driver";
@@ -632,20 +633,31 @@ static int mcs7830_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 static void mcs7830_status(struct usbnet *dev, struct urb *urb)
 {
         u8 *buf = urb->transfer_buffer;
-        bool link;
+        bool link, link_changed;
+        struct mcs7830_data *data = mcs7830_get_data(dev);
 
         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);
-        }
+        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;
+                        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);
+                }
+        } else
+                data->link_counter = 0;
 }
 
 static const struct driver_info moschip_info = {