net: dsa: add ds and index to dsa_port

Add the physical switch instance and port index a DSA port belongs to to
the dsa_port structure.

That can be used later to retrieve information about a physical port
when configuring a switch fabric, or lighten up struct dsa_slave_priv.
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -140,6 +140,8 @@ struct dsa_switch_tree {
 };
 
 struct dsa_port {
+	struct dsa_switch	*ds;
+	unsigned int		index;
 	struct net_device	*netdev;
 	struct device_node	*dn;
 	unsigned int		ageing_time;

net/dsa/dsa2.c

@@ -670,6 +670,7 @@ struct dsa_switch *dsa_switch_alloc(struct device *dev, size_t n)
 {
 	size_t size = sizeof(struct dsa_switch) + n * sizeof(struct dsa_port);
 	struct dsa_switch *ds;
+	int i;
 
 	ds = devm_kzalloc(dev, size, GFP_KERNEL);
 	if (!ds)
@@ -678,6 +679,11 @@ struct dsa_switch *dsa_switch_alloc(struct device *dev, size_t n)
 	ds->dev = dev;
 	ds->num_ports = n;
 
+	for (i = 0; i < ds->num_ports; ++i) {
+		ds->ports[i].index = i;
+		ds->ports[i].ds = ds;
+	}
+
 	return ds;
 }
 EXPORT_SYMBOL_GPL(dsa_switch_alloc);