net: dsa: tag_8021q: refactor RX VLAN parsing into a dedicated function

The added value of this function is that it can deal with both the case
where the VLAN header is in the skb head, as well as in the offload field.
This is something I was not able to do using other functions in the
network stack.

Since both ocelot-8021q and sja1105 need to do the same stuff, let's
make it a common service provided by tag_8021q.

This is done as refactoring for the new SJA1110 tagger, which partly
uses tag_8021q as well (just like SJA1105), and will be the third caller.

Signed-off-by: Vladimir Oltean <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/dsa/8021q.h

···
 struct sk_buff *dsa_8021q_xmit(struct sk_buff *skb, struct net_device *netdev,
 			       u16 tpid, u16 tci);
 
+void dsa_8021q_rcv(struct sk_buff *skb, int *source_port, int *switch_id,
+		   int *subvlan);
+
 u16 dsa_8021q_tx_vid(struct dsa_switch *ds, int port);
 
 u16 dsa_8021q_rx_vid(struct dsa_switch *ds, int port);

net/dsa/tag_8021q.c

···
 }
 EXPORT_SYMBOL_GPL(dsa_8021q_xmit);
 
+void dsa_8021q_rcv(struct sk_buff *skb, int *source_port, int *switch_id,
+		   int *subvlan)
+{
+	u16 vid, tci;
+
+	skb_push_rcsum(skb, ETH_HLEN);
+	if (skb_vlan_tag_present(skb)) {
+		tci = skb_vlan_tag_get(skb);
+		__vlan_hwaccel_clear_tag(skb);
+	} else {
+		__skb_vlan_pop(skb, &tci);
+	}
+	skb_pull_rcsum(skb, ETH_HLEN);
+
+	vid = tci & VLAN_VID_MASK;
+
+	*source_port = dsa_8021q_rx_source_port(vid);
+	*switch_id = dsa_8021q_rx_switch_id(vid);
+	*subvlan = dsa_8021q_rx_subvlan(vid);
+	skb->priority = (tci & VLAN_PRIO_MASK) >> VLAN_PRIO_SHIFT;
+}
+EXPORT_SYMBOL_GPL(dsa_8021q_rcv);
+
 MODULE_LICENSE("GPL v2");

net/dsa/tag_ocelot_8021q.c

···
 				  struct net_device *netdev,
 				  struct packet_type *pt)
 {
-	int src_port, switch_id, qos_class;
-	u16 vid, tci;
+	int src_port, switch_id, subvlan;
 
-	skb_push_rcsum(skb, ETH_HLEN);
-	if (skb_vlan_tag_present(skb)) {
-		tci = skb_vlan_tag_get(skb);
-		__vlan_hwaccel_clear_tag(skb);
-	} else {
-		__skb_vlan_pop(skb, &tci);
-	}
-	skb_pull_rcsum(skb, ETH_HLEN);
-
-	vid = tci & VLAN_VID_MASK;
-	src_port = dsa_8021q_rx_source_port(vid);
-	switch_id = dsa_8021q_rx_switch_id(vid);
-	qos_class = (tci & VLAN_PRIO_MASK) >> VLAN_PRIO_SHIFT;
+	dsa_8021q_rcv(skb, &src_port, &switch_id, &subvlan);
 
 	skb->dev = dsa_master_find_slave(netdev, switch_id, src_port);
 	if (!skb->dev)
 		return NULL;
 
 	skb->offload_fwd_mark = 1;
-	skb->priority = qos_class;
 
 	return skb;
 }

net/dsa/tag_sja1105.c

···
 	__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), vlan_tci);
 }
 
+static bool sja1105_skb_has_tag_8021q(const struct sk_buff *skb)
+{
+	u16 tpid = ntohs(eth_hdr(skb)->h_proto);
+
+	return tpid == ETH_P_SJA1105 || tpid == ETH_P_8021Q ||
+	       skb_vlan_tag_present(skb);
+}
+
 static struct sk_buff *sja1105_rcv(struct sk_buff *skb,
 				   struct net_device *netdev,
 				   struct packet_type *pt)
 {
+	int source_port, switch_id, subvlan = 0;
 	struct sja1105_meta meta = {0};
-	int source_port, switch_id;
 	struct ethhdr *hdr;
-	u16 tpid, vid, tci;
 	bool is_link_local;
-	u16 subvlan = 0;
-	bool is_tagged;
 	bool is_meta;
 
 	hdr = eth_hdr(skb);
-	tpid = ntohs(hdr->h_proto);
-	is_tagged = (tpid == ETH_P_SJA1105 || tpid == ETH_P_8021Q ||
-		     skb_vlan_tag_present(skb));
 	is_link_local = sja1105_is_link_local(skb);
 	is_meta = sja1105_is_meta_frame(skb);
 
 	skb->offload_fwd_mark = 1;
 
-	if (is_tagged) {
+	if (sja1105_skb_has_tag_8021q(skb)) {
 		/* Normal traffic path. */
-		skb_push_rcsum(skb, ETH_HLEN);
-		if (skb_vlan_tag_present(skb)) {
-			tci = skb_vlan_tag_get(skb);
-			__vlan_hwaccel_clear_tag(skb);
-		} else {
-			__skb_vlan_pop(skb, &tci);
-		}
-		skb_pull_rcsum(skb, ETH_HLEN);
-
-		vid = tci & VLAN_VID_MASK;
-		source_port = dsa_8021q_rx_source_port(vid);
-		switch_id = dsa_8021q_rx_switch_id(vid);
-		skb->priority = (tci & VLAN_PRIO_MASK) >> VLAN_PRIO_SHIFT;
-		subvlan = dsa_8021q_rx_subvlan(vid);
+		dsa_8021q_rcv(skb, &source_port, &switch_id, &subvlan);
 	} else if (is_link_local) {
 		/* Management traffic path. Switch embeds the switch ID and
 		 * port ID into bytes of the destination MAC, courtesy of