net: dsa: tag_8021q: introduce a vid_is_dsa_8021q helper

This function returns a boolean denoting whether the VLAN passed as
argument is part of the 1024-3071 range that the dsa_8021q tagging
scheme uses.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/dsa/8021q.h

@@ -50,6 +50,8 @@ int dsa_8021q_rx_switch_id(u16 vid);
 
 int dsa_8021q_rx_source_port(u16 vid);
 
+bool vid_is_dsa_8021q(u16 vid);
+
 #else
 
 int dsa_port_setup_8021q_tagging(struct dsa_switch *ds, int index,
@@ -107,6 +109,11 @@ int dsa_8021q_rx_source_port(u16 vid)
 	return 0;
 }
 
+bool vid_is_dsa_8021q(u16 vid)
+{
+	return false;
+}
+
 #endif /* IS_ENABLED(CONFIG_NET_DSA_TAG_8021Q) */
 
 #endif /* _NET_DSA_8021Q_H */

net/dsa/tag_8021q.c

@@ -93,6 +93,13 @@ int dsa_8021q_rx_source_port(u16 vid)
 }
 EXPORT_SYMBOL_GPL(dsa_8021q_rx_source_port);
 
+bool vid_is_dsa_8021q(u16 vid)
+{
+	return ((vid & DSA_8021Q_DIR_MASK) == DSA_8021Q_DIR_RX ||
+		(vid & DSA_8021Q_DIR_MASK) == DSA_8021Q_DIR_TX);
+}
+EXPORT_SYMBOL_GPL(vid_is_dsa_8021q);
+
 static int dsa_8021q_restore_pvid(struct dsa_switch *ds, int port)
 {
 	struct bridge_vlan_info vinfo;