net: dsa: tag_brcm: Prepare for supporting prepended tag

In preparation for supporting the same Broadcom tag format, but instead
of inserted between the MAC SA and EtherType, prepended to the Ethernet
frame, restructure the code a little bit to make that possible and take
an offset parameter.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/tag_brcm.c

@@ -59,7 +59,9 @@
 #define BRCM_EG_TC_MASK		0x7
 #define BRCM_EG_PID_MASK	0x1f
 
-static struct sk_buff *brcm_tag_xmit(struct sk_buff *skb, struct net_device *dev)
+static struct sk_buff *brcm_tag_xmit_ll(struct sk_buff *skb,
+					struct net_device *dev,
+					unsigned int offset)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
 	u16 queue = skb_get_queue_mapping(skb);
@@ -70,10 +72,10 @@ static struct sk_buff *brcm_tag_xmit(struct sk_buff *skb, struct net_device *dev
 
 	skb_push(skb, BRCM_TAG_LEN);
 
-	memmove(skb->data, skb->data + BRCM_TAG_LEN, 2 * ETH_ALEN);
+	if (offset)
+		memmove(skb->data, skb->data + BRCM_TAG_LEN, offset);
 
-	/* Build the tag after the MAC Source Address */
-	brcm_tag = skb->data + 2 * ETH_ALEN;
+	brcm_tag = skb->data + offset;
 
 	/* Set the ingress opcode, traffic class, tag enforcment is
 	 * deprecated
@@ -94,8 +96,17 @@ static struct sk_buff *brcm_tag_xmit(struct sk_buff *skb, struct net_device *dev
 	return skb;
 }
 
-static struct sk_buff *brcm_tag_rcv(struct sk_buff *skb, struct net_device *dev,
-				    struct packet_type *pt)
+static struct sk_buff *brcm_tag_xmit(struct sk_buff *skb,
+				     struct net_device *dev)
+{
+	/* Build the tag after the MAC Source Address */
+	return brcm_tag_xmit_ll(skb, dev, 2 * ETH_ALEN);
+}
+
+static struct sk_buff *brcm_tag_rcv_ll(struct sk_buff *skb,
+				       struct net_device *dev,
+				       struct packet_type *pt,
+				       unsigned int offset)
 {
 	int source_port;
 	u8 *brcm_tag;
@@ -103,8 +114,7 @@ static struct sk_buff *brcm_tag_rcv(struct sk_buff *skb, struct net_device *dev,
 	if (unlikely(!pskb_may_pull(skb, BRCM_TAG_LEN)))
 		return NULL;
 
-	/* skb->data points to the EtherType, the tag is right before it */
-	brcm_tag = skb->data - 2;
+	brcm_tag = skb->data - offset;
 
 	/* The opcode should never be different than 0b000 */
 	if (unlikely((brcm_tag[0] >> BRCM_OPCODE_SHIFT) & BRCM_OPCODE_MASK))
@@ -126,12 +136,25 @@ static struct sk_buff *brcm_tag_rcv(struct sk_buff *skb, struct net_device *dev,
 	/* Remove Broadcom tag and update checksum */
 	skb_pull_rcsum(skb, BRCM_TAG_LEN);
 
+	return skb;
+}
+
+static struct sk_buff *brcm_tag_rcv(struct sk_buff *skb, struct net_device *dev,
+				    struct packet_type *pt)
+{
+	struct sk_buff *nskb;
+
+	/* skb->data points to the EtherType, the tag is right before it */
+	nskb = brcm_tag_rcv_ll(skb, dev, pt, 2);
+	if (!nskb)
+		return nskb;
+
 	/* Move the Ethernet DA and SA */
-	memmove(skb->data - ETH_HLEN,
-		skb->data - ETH_HLEN - BRCM_TAG_LEN,
+	memmove(nskb->data - ETH_HLEN,
+		nskb->data - ETH_HLEN - BRCM_TAG_LEN,
 		2 * ETH_ALEN);
 
-	return skb;
+	return nskb;
 }
 
 const struct dsa_device_ops brcm_netdev_ops = {