net: dsa: Add helper to resolve bridge port from DSA port

In order for a driver to be able to query a bridge for information
about itself, e.g. reading out port flags, it has to use a netdev that
is known to the bridge. In the simple case, that is just the netdev
representing the port, e.g. swp0 or swp1 in this example:

   br0
   / \
swp0 swp1

But in the case of an offloaded lag, this will be the bond or team
interface, e.g. bond0 in this example:

     br0
     /
  bond0
   / \
swp0 swp1

Add a helper that hides some of this complexity from the
drivers. Then, redefine dsa_port_offloads_bridge_port using the helper
to avoid double accounting of the set of possible offloaded uppers.
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -493,6 +493,20 @@ static inline bool dsa_port_is_vlan_filtering(const struct dsa_port *dp)
 		return dp->vlan_filtering;
 }
 
+static inline
+struct net_device *dsa_port_to_bridge_port(const struct dsa_port *dp)
+{
+	if (!dp->bridge_dev)
+		return NULL;
+
+	if (dp->lag_dev)
+		return dp->lag_dev;
+	else if (dp->hsr_dev)
+		return dp->hsr_dev;
+
+	return dp->slave;
+}
+
 typedef int dsa_fdb_dump_cb_t(const unsigned char *addr, u16 vid,
 			      bool is_static, void *data);
 struct dsa_switch_ops {

net/dsa/dsa_priv.h

@@ -233,19 +233,7 @@ extern const struct phylink_mac_ops dsa_port_phylink_mac_ops;
 static inline bool dsa_port_offloads_bridge_port(struct dsa_port *dp,
 						 struct net_device *dev)
 {
-	/* Switchdev offloading can be configured on: */
-
-	if (dev == dp->slave)
-		/* DSA ports directly connected to a bridge, and event
-		 * was emitted for the ports themselves.
-		 */
-		return true;
-
-	if (dp->lag_dev == dev)
-		/* DSA ports connected to a bridge via a LAG */
-		return true;
-
-	return false;
+	return dsa_port_to_bridge_port(dp) == dev;
 }
 
 static inline bool dsa_port_offloads_bridge(struct dsa_port *dp,