net/mlx5e: Update and set Xon/Xoff upon MTU set

Xon/Xoff sizes are derived from calculation that include the MTU size.
Set Xon/Xoff when MTU is set.
If Xon/Xoff fails, set the previous MTU.

Fixes: 0696d60 ("net/mlx5e: Receive buffer configuration")
Signed-off-by: Alexei Lazar <alazar@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Link: https://patch.msgid.link/20250825143435.598584-10-mbloch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Alexei Lazar

drivers/net/ethernet/mellanox/mlx5/core/en/port_buffer.h

@@ -66,11 +66,23 @@ struct mlx5e_port_buffer {
 	struct mlx5e_bufferx_reg  buffer[MLX5E_MAX_NETWORK_BUFFER];
 };
 
+#ifdef CONFIG_MLX5_CORE_EN_DCB
 int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 				    u32 change, unsigned int mtu,
 				    struct ieee_pfc *pfc,
 				    u32 *buffer_size,
 				    u8 *prio2buffer);
+#else
+static inline int
+mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
+				u32 change, unsigned int mtu,
+				void *pfc,
+				u32 *buffer_size,
+				u8 *prio2buffer)
+{
+	return 0;
+}
+#endif
 
 int mlx5e_port_query_buffer(struct mlx5e_priv *priv,
 			    struct mlx5e_port_buffer *port_buffer);

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

@@ -49,6 +49,7 @@
 #include "en.h"
 #include "en/dim.h"
 #include "en/txrx.h"
+#include "en/port_buffer.h"
 #include "en_tc.h"
 #include "en_rep.h"
 #include "en_accel/ipsec.h"
@@ -3040,9 +3041,11 @@ int mlx5e_set_dev_port_mtu(struct mlx5e_priv *priv)
 	struct mlx5e_params *params = &priv->channels.params;
 	struct net_device *netdev = priv->netdev;
 	struct mlx5_core_dev *mdev = priv->mdev;
-	u16 mtu;
+	u16 mtu, prev_mtu;
 	int err;
 
+	mlx5e_query_mtu(mdev, params, &prev_mtu);
+
 	err = mlx5e_set_mtu(mdev, params, params->sw_mtu);
 	if (err)
 		return err;
@@ -3052,6 +3055,18 @@ int mlx5e_set_dev_port_mtu(struct mlx5e_priv *priv)
 		netdev_warn(netdev, "%s: VPort MTU %d is different than netdev mtu %d\n",
 			    __func__, mtu, params->sw_mtu);
 
+	if (mtu != prev_mtu && MLX5_BUFFER_SUPPORTED(mdev)) {
+		err = mlx5e_port_manual_buffer_config(priv, 0, mtu,
+						      NULL, NULL, NULL);
+		if (err) {
+			netdev_warn(netdev, "%s: Failed to set Xon/Xoff values with MTU %d (err %d), setting back to previous MTU %d\n",
+				    __func__, mtu, err, prev_mtu);
+
+			mlx5e_set_mtu(mdev, params, prev_mtu);
+			return err;
+		}
+	}
+
 	params->sw_mtu = mtu;
 	return 0;
 }