hv_netvsc: Cache the current data path to avoid duplicate call and message

The previous change "hv_netvsc: Switch the data path at the right time
during hibernation" adds the call of netvsc_vf_changed() upon
NETDEV_CHANGE, so it's necessary to avoid the duplicate call and message
when the VF is brought UP or DOWN.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -974,6 +974,9 @@ struct net_device_context {
 	/* Serial number of the VF to team with */
 	u32 vf_serial;
 
+	/* Is the current data path through the VF NIC? */
+	bool  data_path_is_vf;
+
 	/* Used to temporarily save the config info across hibernation */
 	struct netvsc_device_info *saved_netvsc_dev_info;
 };

drivers/net/hyperv/netvsc_drv.c

@@ -2366,7 +2366,16 @@ static int netvsc_register_vf(struct net_device *vf_netdev)
 	return NOTIFY_OK;
 }
 
-/* VF up/down change detected, schedule to change data path */
+/* Change the data path when VF UP/DOWN/CHANGE are detected.
+ *
+ * Typically a UP or DOWN event is followed by a CHANGE event, so
+ * net_device_ctx->data_path_is_vf is used to cache the current data path
+ * to avoid the duplicate call of netvsc_switch_datapath() and the duplicate
+ * message.
+ *
+ * During hibernation, if a VF NIC driver (e.g. mlx5) preserves the network
+ * interface, there is only the CHANGE event and no UP or DOWN event.
+ */
 static int netvsc_vf_changed(struct net_device *vf_netdev)
 {
 	struct net_device_context *net_device_ctx;
@@ -2383,6 +2392,10 @@ static int netvsc_vf_changed(struct net_device *vf_netdev)
 	if (!netvsc_dev)
 		return NOTIFY_DONE;
 
+	if (net_device_ctx->data_path_is_vf == vf_is_up)
+		return NOTIFY_OK;
+	net_device_ctx->data_path_is_vf = vf_is_up;
+
 	netvsc_switch_datapath(ndev, vf_is_up);
 	netdev_info(ndev, "Data path switched %s VF: %s\n",
 		    vf_is_up ? "to" : "from", vf_netdev->name);
@@ -2624,6 +2637,12 @@ static int netvsc_resume(struct hv_device *dev)
 	rtnl_lock();
 
 	net_device_ctx = netdev_priv(net);
+
+	/* Reset the data path to the netvsc NIC before re-opening the vmbus
+	 * channel. Later netvsc_netdev_event() will switch the data path to
+	 * the VF upon the UP or CHANGE event.
+	 */
+	net_device_ctx->data_path_is_vf = false;
 	device_info = net_device_ctx->saved_netvsc_dev_info;
 
 	ret = netvsc_attach(net, device_info);