drivers: net: cpsw: fix suspend when all ethX devices are down

BugLink: http://bugs.launchpad.net/bugs/1625177

The cpsw_suspend() could trigger L3 error and CPSW will stop
functioning if System enters suspend when all ethX net-devices are
down - in this case CPSW could be already suspended by PM runtime, but
cpsw_suspend() will try to call soft_reset_slave() unconditionally
and access CPSW registers.

Hence, fix it by moving soft_reset_slave() from cpsw_suspend() to
cpsw_slave_stop(). This way slave ports will be reset when CPSW is
active and will be in proper state during Suspend.
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 1f95ba00)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/net/ethernet/ti/cpsw.c

@@ -1243,6 +1243,7 @@ static void cpsw_slave_stop(struct cpsw_slave *slave, struct cpsw_priv *priv)
 	slave->phy = NULL;
 	cpsw_ale_control_set(priv->ale, slave_port,
 			     ALE_PORT_STATE, ALE_PORT_STATE_DISABLE);
+	soft_reset_slave(slave);
 }
 
 static int cpsw_ndo_open(struct net_device *ndev)
@@ -2561,12 +2562,10 @@ static int cpsw_suspend(struct device *dev)
 		for (i = 0; i < priv->data.slaves; i++) {
 			if (netif_running(priv->slaves[i].ndev))
 				cpsw_ndo_stop(priv->slaves[i].ndev);
-			soft_reset_slave(priv->slaves + i);
 		}
 	} else {
 		if (netif_running(ndev))
 			cpsw_ndo_stop(ndev);
-		for_each_slave(priv, soft_reset_slave);
 	}
 
 	pm_runtime_put_sync(&pdev->dev);