[PATCH] [xenial] [PATCH] (upstream) net/mlx5e: Fix minimum MTU

[Talat Batheesh]

From: Saeed Mahameed <saeedm at mellanox.com>

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1528466

Minimum MTU that can be set in Connectx4 device is 68.

This fixes the case where a user wants to set invalid MTU,
the driver will fail to satisfy this request and the interface
will stay down.

It is better to report an error and continue working with old
mtu.

Signed-off-by: Saeed Mahameed <saeedm at mellanox.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit d8edd2469ace550db707798180d1c84d81f93bca upstream)
Signed-off-by: Talat Batheesh <talatb at mellanox.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index 9923450..5feb124 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -1890,22 +1890,27 @@ static int mlx5e_set_features(struct net_device *netdev,
 	return err;
 }
 
+#define MXL5_HW_MIN_MTU 64
+#define MXL5E_MIN_MTU (MXL5_HW_MIN_MTU + ETH_FCS_LEN)
+
 static int mlx5e_change_mtu(struct net_device *netdev, int new_mtu)
 {
 	struct mlx5e_priv *priv = netdev_priv(netdev);
 	struct mlx5_core_dev *mdev = priv->mdev;
 	bool was_opened;
-	int max_mtu;
+	u16 max_mtu;
+	u16 min_mtu;
 	int err = 0;
 
 	mlx5_query_port_max_mtu(mdev, &max_mtu, 1);
 
 	max_mtu = MLX5E_HW2SW_MTU(max_mtu);
+	min_mtu = MLX5E_HW2SW_MTU(MXL5E_MIN_MTU);
 
-	if (new_mtu > max_mtu) {
+	if (new_mtu > max_mtu || new_mtu < min_mtu) {
 		netdev_err(netdev,
-			   "%s: Bad MTU (%d) > (%d) Max\n",
-			   __func__, new_mtu, max_mtu);
+			   "%s: Bad MTU (%d), valid range is: [%d..%d]\n",
+			   __func__, new_mtu, min_mtu, max_mtu);
 		return -EINVAL;
 	}
 
-- 
2.5.0