net/mlx5e: Don't try to modify CQ moderation if it is not supported

BugLink: http://bugs.launchpad.net/bugs/1557950

If CQ moderation is not supported by the device, print a warning on
netdevice load, and return error when trying to modify/query cq
moderation via ethtool.

Fixes: f62b8bb8 ('net/mlx5: Extend mlx5_core to support ConnectX-4
Ethernet functionality')
Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from linux-next commit 7524a5d8)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c

@@ -399,6 +399,9 @@ static int mlx5e_get_coalesce(struct net_device *netdev,
 {
 	struct mlx5e_priv *priv = netdev_priv(netdev);
 
+	if (!MLX5_CAP_GEN(priv->mdev, cq_moderation))
+		return -ENOTSUPP;
+
 	coal->rx_coalesce_usecs       = priv->params.rx_cq_moderation_usec;
 	coal->rx_max_coalesced_frames = priv->params.rx_cq_moderation_pkts;
 	coal->tx_coalesce_usecs       = priv->params.tx_cq_moderation_usec;
@@ -416,6 +419,9 @@ static int mlx5e_set_coalesce(struct net_device *netdev,
 	int tc;
 	int i;
 
+	if (!MLX5_CAP_GEN(mdev, cq_moderation))
+		return -ENOTSUPP;
+
 	priv->params.tx_cq_moderation_usec = coal->tx_coalesce_usecs;
 	priv->params.tx_cq_moderation_pkts = coal->tx_max_coalesced_frames;
 	priv->params.rx_cq_moderation_usec = coal->rx_coalesce_usecs;

drivers/net/ethernet/mellanox/mlx5/core/en_main.c

@@ -864,12 +864,10 @@ static int mlx5e_open_cq(struct mlx5e_channel *c,
 	if (err)
 		goto err_destroy_cq;
 
-	err = mlx5_core_modify_cq_moderation(mdev, &cq->mcq,
-					     moderation_usecs,
-					     moderation_frames);
-	if (err)
-		goto err_destroy_cq;
-
+	if (MLX5_CAP_GEN(mdev, cq_moderation))
+		mlx5_core_modify_cq_moderation(mdev, &cq->mcq,
+					       moderation_usecs,
+					       moderation_frames);
 	return 0;
 
 err_destroy_cq:
@@ -2032,6 +2030,8 @@ static int mlx5e_check_required_hca_cap(struct mlx5_core_dev *mdev)
 	}
 	if (!MLX5_CAP_ETH(mdev, self_lb_en_modifiable))
 		mlx5_core_warn(mdev, "Self loop back prevention is not supported\n");
+	if (!MLX5_CAP_GEN(mdev, cq_moderation))
+		mlx5_core_warn(mdev, "CQ modiration is not supported\n");
 
 	return 0;
 }