net: dsa: populate supported_interfaces member

Add a new DSA switch operation, phylink_get_interfaces, which should
fill in which PHY_INTERFACE_MODE_* are supported by given port.

Use this before phylink_create() to fill phylinks supported_interfaces
member, allowing phylink to determine which PHY_INTERFACE_MODEs are
supported.
Signed-off-by: Marek Behún <kabel@kernel.org>
[tweaked patch and description to add more complete support -- rmk]
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -645,6 +645,8 @@ struct dsa_switch_ops {
 	/*
 	 * PHYLINK integration
 	 */
+	void	(*phylink_get_interfaces)(struct dsa_switch *ds, int port,
+					  unsigned long *supported_interfaces);
 	void	(*phylink_validate)(struct dsa_switch *ds, int port,
 				    unsigned long *supported,
 				    struct phylink_link_state *state);

net/dsa/port.c

@@ -1168,6 +1168,10 @@ static int dsa_port_phylink_register(struct dsa_port *dp)
 	dp->pl_config.type = PHYLINK_DEV;
 	dp->pl_config.pcs_poll = ds->pcs_poll;
 
+	if (ds->ops->phylink_get_interfaces)
+		ds->ops->phylink_get_interfaces(ds, dp->index,
+					dp->pl_config.supported_interfaces);
+
 	dp->pl = phylink_create(&dp->pl_config, of_fwnode_handle(port_dn),
 				mode, &dsa_port_phylink_mac_ops);
 	if (IS_ERR(dp->pl)) {

net/dsa/slave.c

@@ -1871,6 +1871,10 @@ static int dsa_slave_phy_setup(struct net_device *slave_dev)
 		dp->pl_config.poll_fixed_state = true;
 	}
 
+	if (ds->ops->phylink_get_interfaces)
+		ds->ops->phylink_get_interfaces(ds, dp->index,
+					dp->pl_config.supported_interfaces);
+
 	dp->pl = phylink_create(&dp->pl_config, of_fwnode_handle(port_dn), mode,
 				&dsa_port_phylink_mac_ops);
 	if (IS_ERR(dp->pl)) {