net: bridge: mst: Add helper to check if MST is enabled

This is useful for switchdev drivers that might want to refuse to join
a bridge where MST is enabled, if the hardware can't support it.
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/if_bridge.h

@@ -119,6 +119,7 @@ int br_vlan_get_info(const struct net_device *dev, u16 vid,
 		     struct bridge_vlan_info *p_vinfo);
 int br_vlan_get_info_rcu(const struct net_device *dev, u16 vid,
 			 struct bridge_vlan_info *p_vinfo);
+bool br_mst_enabled(const struct net_device *dev);
 int br_mst_get_info(const struct net_device *dev, u16 msti, unsigned long *vids);
 #else
 static inline bool br_vlan_enabled(const struct net_device *dev)
@@ -153,6 +154,11 @@ static inline int br_vlan_get_info_rcu(const struct net_device *dev, u16 vid,
 	return -EINVAL;
 }
 
+static inline bool br_mst_enabled(const struct net_device *dev)
+{
+	return false;
+}
+
 static inline int br_mst_get_info(const struct net_device *dev, u16 msti,
 				  unsigned long *vids)
 {

net/bridge/br_mst.c

@@ -13,6 +13,15 @@
 
 DEFINE_STATIC_KEY_FALSE(br_mst_used);
 
+bool br_mst_enabled(const struct net_device *dev)
+{
+	if (!netif_is_bridge_master(dev))
+		return false;
+
+	return br_opt_get(netdev_priv(dev), BROPT_MST_ENABLED);
+}
+EXPORT_SYMBOL_GPL(br_mst_enabled);
+
 int br_mst_get_info(const struct net_device *dev, u16 msti, unsigned long *vids)
 {
 	const struct net_bridge_vlan_group *vg;