net: dsa: allow switch drivers to implement suspend/resume hooks

Add an abstraction layer to suspend/resume switch devices, doing the
following split:

- suspend/resume the slave network devices and their corresponding PHY
  devices
- suspend/resume the switch hardware using switch driver callbacks

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index a799726..143811e 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -412,6 +412,37 @@
 			p->phy->addr, p->phy->drv->name);
 }
 
+int dsa_slave_suspend(struct net_device *slave_dev)
+{
+	struct dsa_slave_priv *p = netdev_priv(slave_dev);
+
+	netif_device_detach(slave_dev);
+
+	if (p->phy) {
+		phy_stop(p->phy);
+		p->old_pause = -1;
+		p->old_link = -1;
+		p->old_duplex = -1;
+		phy_suspend(p->phy);
+	}
+
+	return 0;
+}
+
+int dsa_slave_resume(struct net_device *slave_dev)
+{
+	struct dsa_slave_priv *p = netdev_priv(slave_dev);
+
+	netif_device_attach(slave_dev);
+
+	if (p->phy) {
+		phy_resume(p->phy);
+		phy_start(p->phy);
+	}
+
+	return 0;
+}
+
 struct net_device *
 dsa_slave_create(struct dsa_switch *ds, struct device *parent,
 		 int port, char *name)