net: dsa: allow switches to work without tagging

In case switch port tagging is disabled (voluntarily, or the switch just
does not support it), allow us to continue using the defined set of
dsa_device_ops in net/dsa/slave.c.

We introduce dsa_protocol_is_tagged() to check whether we need to
override skb->protocol and go through the DSA-specifif packet_type
function, or if we just go on and receive the SKB through the normal
path.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1784,10 +1784,10 @@ void dev_net_set(struct net_device *dev, struct net *net)
 static inline bool netdev_uses_dsa(struct net_device *dev)
 {
 #ifdef CONFIG_NET_DSA
-	return dev->dsa_ptr != NULL;
-#else
-	return false;
+	if (dev->dsa_ptr != NULL)
+		return dsa_uses_tagged_protocol(dev->dsa_ptr);
 #endif
+	return false;
 }
 
 /**

include/net/dsa.h

@@ -198,4 +198,9 @@ static inline void *ds_to_priv(struct dsa_switch *ds)
 	return (void *)(ds + 1);
 }
 
+static inline bool dsa_uses_tagged_protocol(struct dsa_switch_tree *dst)
+{
+	return dst->tag_protocol != 0;
+}
+
 #endif

net/dsa/slave.c

@@ -181,6 +181,17 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
 	return dst->ops->xmit(skb, dev);
 }
 
+static netdev_tx_t dsa_slave_notag_xmit(struct sk_buff *skb,
+					struct net_device *dev)
+{
+	struct dsa_slave_priv *p = netdev_priv(dev);
+
+	skb->dev = p->parent->dst->master_netdev;
+	dev_queue_xmit(skb);
+
+	return NETDEV_TX_OK;
+}
+
 
 /* ethtool operations *******************************************************/
 static int
@@ -314,6 +325,11 @@ static const struct net_device_ops dsa_slave_netdev_ops = {
 	.ndo_do_ioctl		= dsa_slave_ioctl,
 };
 
+static const struct dsa_device_ops notag_netdev_ops = {
+	.xmit	= dsa_slave_notag_xmit,
+	.rcv	= NULL,
+};
+
 static void dsa_slave_adjust_link(struct net_device *dev)
 {
 	struct dsa_slave_priv *p = netdev_priv(dev);
@@ -415,7 +431,8 @@ dsa_slave_create(struct dsa_switch *ds, struct device *parent,
 		break;
 #endif
 	default:
-		BUG();
+		ds->dst->ops = &notag_netdev_ops;
+		break;
 	}
 
 	SET_NETDEV_DEV(slave_dev, parent);