[PATCH 4.2 08/54] net: dsa: fix preparation of a port STP update

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vivien Didelot <vivien.didelot@savoirfairelinux.com>

[ Upstream commit 57a47532c4312159935c98b7f1cf0e62296b9171 ]

Because of the default 0 value of ret in dsa_slave_port_attr_set, a
driver may return -EOPNOTSUPP from the commit phase of a STP state,
which triggers a WARN() from switchdev.

This happened on a 6185 switch which does not support hardware bridging.

Fixes: 3563606258cf ("switchdev: convert STP update to switchdev attr set")
Reported-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/dsa/slave.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -348,12 +348,17 @@ static int dsa_slave_stp_update(struct n
 static int dsa_slave_port_attr_set(struct net_device *dev,
 				   struct switchdev_attr *attr)
 {
-	int ret = 0;
+	struct dsa_slave_priv *p = netdev_priv(dev);
+	struct dsa_switch *ds = p->parent;
+	int ret;
 
 	switch (attr->id) {
 	case SWITCHDEV_ATTR_PORT_STP_STATE:
-		if (attr->trans == SWITCHDEV_TRANS_COMMIT)
-			ret = dsa_slave_stp_update(dev, attr->u.stp_state);
+		if (attr->trans == SWITCHDEV_TRANS_PREPARE)
+			ret = ds->drv->port_stp_update ? 0 : -EOPNOTSUPP;
+		else
+			ret = ds->drv->port_stp_update(ds, p->port,
+						       attr->u.stp_state);
 		break;
 	default:
 		ret = -EOPNOTSUPP;