mlxsw: spectrum_router: Handle MTU change of GRE netdevs

Update MTU of overlay loopback in accordance with the setting on the
tunnel netdevice.

Fixes: 0063587d ("mlxsw: spectrum: Support decap-only IP-in-IP tunnels")
Signed-off-by: NPetr Machata <petrm@mellanox.com>
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c

@@ -1407,6 +1407,28 @@ mlxsw_sp_rif_ipip_lb_op(struct mlxsw_sp_rif_ipip_lb *lb_rif,
 	return mlxsw_reg_write(mlxsw_sp->core, MLXSW_REG(ritr), ritr_pl);
 }
 
+static int mlxsw_sp_netdevice_ipip_ol_update_mtu(struct mlxsw_sp *mlxsw_sp,
+						 struct net_device *ol_dev)
+{
+	struct mlxsw_sp_ipip_entry *ipip_entry;
+	struct mlxsw_sp_rif_ipip_lb *lb_rif;
+	struct mlxsw_sp_vr *ul_vr;
+	int err = 0;
+
+	ipip_entry = mlxsw_sp_ipip_entry_find_by_ol_dev(mlxsw_sp, ol_dev);
+	if (ipip_entry) {
+		lb_rif = ipip_entry->ol_lb;
+		ul_vr = &mlxsw_sp->router->vrs[lb_rif->ul_vr_id];
+		err = mlxsw_sp_rif_ipip_lb_op(lb_rif, ul_vr, true);
+		if (err)
+			goto out;
+		lb_rif->common.mtu = ol_dev->mtu;
+	}
+
+out:
+	return err;
+}
+
 static void mlxsw_sp_netdevice_ipip_ol_up_event(struct mlxsw_sp *mlxsw_sp,
 						struct net_device *ol_dev)
 {
@@ -1687,6 +1709,8 @@ int mlxsw_sp_netdevice_ipip_ol_event(struct mlxsw_sp *mlxsw_sp,
 		extack = info->extack;
 		return mlxsw_sp_netdevice_ipip_ol_change_event(mlxsw_sp,
 							       ol_dev, extack);
+	case NETDEV_CHANGEMTU:
+		return mlxsw_sp_netdevice_ipip_ol_update_mtu(mlxsw_sp, ol_dev);
 	}
 	return 0;
 }