net: dsa: tag_ksz: do not rely on skb_mac_header() in TX paths

skb_mac_header() will no longer be available in the TX path when
reverting commit 6d1ccff ("net: reset mac header in
dev_start_xmit()"). As preparation for that, let's use skb_eth_hdr() to
get to the Ethernet header's MAC DA instead, helper which assumes this
header is located at skb->data (assumption which holds true here).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: vladimiroltean

net/dsa/tag_ksz.c

@@ -120,18 +120,18 @@ static struct sk_buff *ksz_common_rcv(struct sk_buff *skb,
 static struct sk_buff *ksz8795_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
+	struct ethhdr *hdr;
 	u8 *tag;
-	u8 *addr;
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))
 		return NULL;
 
 	/* Tag encoding */
 	tag = skb_put(skb, KSZ_INGRESS_TAG_LEN);
-	addr = skb_mac_header(skb);
+	hdr = skb_eth_hdr(skb);
 
 	*tag = 1 << dp->index;
-	if (is_link_local_ether_addr(addr))
+	if (is_link_local_ether_addr(hdr->h_dest))
 		*tag |= KSZ8795_TAIL_TAG_OVERRIDE;
 
 	return skb;
@@ -273,8 +273,8 @@ static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
 	u16 queue_mapping = skb_get_queue_mapping(skb);
 	u8 prio = netdev_txq_to_tc(dev, queue_mapping);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
+	struct ethhdr *hdr;
 	__be16 *tag;
-	u8 *addr;
 	u16 val;
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))
@@ -284,13 +284,13 @@ static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
 	ksz_xmit_timestamp(dp, skb);
 
 	tag = skb_put(skb, KSZ9477_INGRESS_TAG_LEN);
-	addr = skb_mac_header(skb);
+	hdr = skb_eth_hdr(skb);
 
 	val = BIT(dp->index);
 
 	val |= FIELD_PREP(KSZ9477_TAIL_TAG_PRIO, prio);
 
-	if (is_link_local_ether_addr(addr))
+	if (is_link_local_ether_addr(hdr->h_dest))
 		val |= KSZ9477_TAIL_TAG_OVERRIDE;
 
 	*tag = cpu_to_be16(val);
@@ -337,7 +337,7 @@ static struct sk_buff *ksz9893_xmit(struct sk_buff *skb,
 	u16 queue_mapping = skb_get_queue_mapping(skb);
 	u8 prio = netdev_txq_to_tc(dev, queue_mapping);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
-	u8 *addr;
+	struct ethhdr *hdr;
 	u8 *tag;
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))
@@ -347,13 +347,13 @@ static struct sk_buff *ksz9893_xmit(struct sk_buff *skb,
 	ksz_xmit_timestamp(dp, skb);
 
 	tag = skb_put(skb, KSZ_INGRESS_TAG_LEN);
-	addr = skb_mac_header(skb);
+	hdr = skb_eth_hdr(skb);
 
 	*tag = BIT(dp->index);
 
 	*tag |= FIELD_PREP(KSZ9893_TAIL_TAG_PRIO, prio);
 
-	if (is_link_local_ether_addr(addr))
+	if (is_link_local_ether_addr(hdr->h_dest))
 		*tag |= KSZ9893_TAIL_TAG_OVERRIDE;
 
 	return ksz_defer_xmit(dp, skb);