Revert "net: dsa: stop updating master MTU from master.c"

This reverts commit a1ff94c2973c43bc1e2677ac63ebb15b1d1ff846.

Switch drivers that don't implement ->port_change_mtu() will cause the
DSA master to remain with an MTU of 1500, since we've deleted the other
code path. In turn, this causes a regression for those systems, where
MTU-sized traffic can no longer be terminated.

Revert the change taking into account the fact that rtnl_lock() is now
taken top-level from the callers of dsa_master_setup() and
dsa_master_teardown(). Also add a comment in order for it to be
absolutely clear why it is still needed.

Fixes: a1ff94c2973c ("net: dsa: stop updating master MTU from master.c")
Reported-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/dsa/master.c b/net/dsa/master.c
index 991c293..2851e44 100644 (file)
--- a/net/dsa/master.c
+++ b/net/dsa/master.c
@@ -335,11 +335,24 @@ static const struct attribute_group dsa_group = {
        .attrs  = dsa_slave_attrs,
 };
 
+static void dsa_master_reset_mtu(struct net_device *dev)
+{
+       int err;
+
+       err = dev_set_mtu(dev, ETH_DATA_LEN);
+       if (err)
+               netdev_dbg(dev,
+                          "Unable to reset MTU to exclude DSA overheads\n");
+}
+
 int dsa_master_setup(struct net_device *dev, struct dsa_port *cpu_dp)
 {
+       const struct dsa_device_ops *tag_ops = cpu_dp->tag_ops;
        struct dsa_switch *ds = cpu_dp->ds;
        struct device_link *consumer_link;
-       int ret;
+       int mtu, ret;
+
+       mtu = ETH_DATA_LEN + dsa_tag_protocol_overhead(tag_ops);
 
        /* The DSA master must use SET_NETDEV_DEV for this to work. */
        consumer_link = device_link_add(ds->dev, dev->dev.parent,
@@ -349,6 +362,15 @@ int dsa_master_setup(struct net_device *dev, struct dsa_port *cpu_dp)
                           "Failed to create a device link to DSA switch %s\n",
                           dev_name(ds->dev));
 
+       /* The switch driver may not implement ->port_change_mtu(), case in
+        * which dsa_slave_change_mtu() will not update the master MTU either,
+        * so we need to do that here.
+        */
+       ret = dev_set_mtu(dev, mtu);
+       if (ret)
+               netdev_warn(dev, "error %d setting MTU to %d to include DSA overhead\n",
+                           ret, mtu);
+
        /* If we use a tagging format that doesn't have an ethertype
         * field, make sure that all packets from this point on get
         * sent to the tag format's receive function.
@@ -384,6 +406,7 @@ void dsa_master_teardown(struct net_device *dev)
        sysfs_remove_group(&dev->dev.kobj, &dsa_group);
        dsa_netdev_ops_set(dev, NULL);
        dsa_master_ethtool_teardown(dev);
+       dsa_master_reset_mtu(dev);
        dsa_master_set_promiscuity(dev, -1);
 
        dev->dsa_ptr = NULL;