ionic: add support for ethtool extended stat link_down_count

Following the example of 'commit 9a0f830f ("ethtool: linkstate:
add a statistic for PHY down events")', added support for link down
events.

Add callback ionic_get_link_ext_stats to ionic_ethtool.c to support
link_down_count, a property of netdev that gets reported exclusively
on physical link down events.

Run ethtool -I <devname> to display the device link down count.
Signed-off-by: Nitya Sunkad <nitya.sunkad@amd.com>
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/pensando/ionic/ionic_ethtool.c

@@ -104,6 +104,15 @@ static void ionic_get_regs(struct net_device *netdev, struct ethtool_regs *regs,
 	memcpy_fromio(p + offset, lif->ionic->idev.dev_cmd_regs->words, size);
 }
 
+static void ionic_get_link_ext_stats(struct net_device *netdev,
+				     struct ethtool_link_ext_stats *stats)
+{
+	struct ionic_lif *lif = netdev_priv(netdev);
+
+	if (lif->ionic->pdev->is_physfn)
+		stats->link_down_events = lif->link_down_count;
+}
+
 static int ionic_get_link_ksettings(struct net_device *netdev,
 				    struct ethtool_link_ksettings *ks)
 {
@@ -1074,6 +1083,7 @@ static const struct ethtool_ops ionic_ethtool_ops = {
 	.get_regs_len		= ionic_get_regs_len,
 	.get_regs		= ionic_get_regs,
 	.get_link		= ethtool_op_get_link,
+	.get_link_ext_stats	= ionic_get_link_ext_stats,
 	.get_link_ksettings	= ionic_get_link_ksettings,
 	.set_link_ksettings	= ionic_set_link_ksettings,
 	.get_coalesce		= ionic_get_coalesce,

drivers/net/ethernet/pensando/ionic/ionic_lif.c

@@ -168,6 +168,7 @@ static void ionic_link_status_check(struct ionic_lif *lif)
 		}
 	} else {
 		if (netif_carrier_ok(netdev)) {
+			lif->link_down_count++;
 			netdev_info(netdev, "Link down\n");
 			netif_carrier_off(netdev);
 		}

drivers/net/ethernet/pensando/ionic/ionic_lif.h

@@ -201,6 +201,7 @@ struct ionic_lif {
 	u64 hw_features;
 	bool registered;
 	u16 lif_type;
+	unsigned int link_down_count;
 	unsigned int nmcast;
 	unsigned int nucast;
 	unsigned int nvlans;