net: dsa: tag_sja1105: refactor skb->dev assignment to dsa_tag_8021q_find_user()

A new tagging protocol implementation based on tag_8021q is on the
horizon, and it appears that it also has to open-code the complicated
logic of finding a source port based on a VLAN header.

Create a single dsa_tag_8021q_find_user() and make sja1105 call it.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20240713211620.1125910-7-paweldembicki@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/tag_8021q.c

@@ -468,8 +468,8 @@ struct sk_buff *dsa_8021q_xmit(struct sk_buff *skb, struct net_device *netdev,
 }
 EXPORT_SYMBOL_GPL(dsa_8021q_xmit);
 
-struct net_device *dsa_tag_8021q_find_port_by_vbid(struct net_device *conduit,
-						   int vbid)
+static struct net_device *
+dsa_tag_8021q_find_port_by_vbid(struct net_device *conduit, int vbid)
 {
 	struct dsa_port *cpu_dp = conduit->dsa_ptr;
 	struct dsa_switch_tree *dst = cpu_dp->dst;
@@ -495,7 +495,20 @@ struct net_device *dsa_tag_8021q_find_port_by_vbid(struct net_device *conduit,
 
 	return NULL;
 }
-EXPORT_SYMBOL_GPL(dsa_tag_8021q_find_port_by_vbid);
+
+struct net_device *dsa_tag_8021q_find_user(struct net_device *conduit,
+					   int source_port, int switch_id,
+					   int vid, int vbid)
+{
+	/* Always prefer precise source port information, if available */
+	if (source_port != -1 && switch_id != -1)
+		return dsa_conduit_find_user(conduit, switch_id, source_port);
+	else if (vbid >= 1)
+		return dsa_tag_8021q_find_port_by_vbid(conduit, vbid);
+
+	return dsa_find_designated_bridge_port_by_vid(conduit, vid);
+}
+EXPORT_SYMBOL_GPL(dsa_tag_8021q_find_user);
 
 /**
  * dsa_8021q_rcv - Decode source information from tag_8021q header

net/dsa/tag_8021q.h

@@ -16,8 +16,9 @@ struct sk_buff *dsa_8021q_xmit(struct sk_buff *skb, struct net_device *netdev,
 void dsa_8021q_rcv(struct sk_buff *skb, int *source_port, int *switch_id,
 		   int *vbid, int *vid);
 
-struct net_device *dsa_tag_8021q_find_port_by_vbid(struct net_device *conduit,
-						   int vbid);
+struct net_device *dsa_tag_8021q_find_user(struct net_device *conduit,
+					   int source_port, int switch_id,
+					   int vid, int vbid);
 
 int dsa_switch_tag_8021q_vlan_add(struct dsa_switch *ds,
 				  struct dsa_notifier_tag_8021q_vlan_info *info);

net/dsa/tag_sja1105.c

@@ -509,12 +509,8 @@ static struct sk_buff *sja1105_rcv(struct sk_buff *skb,
 		 */
 		return NULL;
 
-	if (source_port != -1 && switch_id != -1)
-		skb->dev = dsa_conduit_find_user(netdev, switch_id, source_port);
-	else if (vbid >= 1)
-		skb->dev = dsa_tag_8021q_find_port_by_vbid(netdev, vbid);
-	else
-		skb->dev = dsa_find_designated_bridge_port_by_vid(netdev, vid);
+	skb->dev = dsa_tag_8021q_find_user(netdev, source_port, switch_id,
+					   vid, vbid);
 	if (!skb->dev) {
 		netdev_warn(netdev, "Couldn't decode source port\n");
 		return NULL;
@@ -652,12 +648,9 @@ static struct sk_buff *sja1110_rcv(struct sk_buff *skb,
 	if (likely(sja1105_skb_has_tag_8021q(skb)))
 		dsa_8021q_rcv(skb, &source_port, &switch_id, &vbid, &vid);
 
-	if (source_port != -1 && switch_id != -1)
-		skb->dev = dsa_conduit_find_user(netdev, switch_id, source_port);
-	else if (vbid >= 1)
-		skb->dev = dsa_tag_8021q_find_port_by_vbid(netdev, vbid);
-	else
-		skb->dev = dsa_find_designated_bridge_port_by_vid(netdev, vid);
+	skb->dev = dsa_tag_8021q_find_user(netdev, source_port, switch_id,
+					   vid, vbid);
+
 	if (!skb->dev) {
 		netdev_warn(netdev, "Couldn't decode source port\n");
 		return NULL;