net/mlx5e: Update xon formula

[ Upstream commit e28408e98bced123038857b6e3c81fa12a2e3e68 ]

Set xon = xoff - netdev's max_mtu.
netdev's max_mtu will give enough time for the pause frame to
arrive at the sender.

Fixes: 0696d608 ("net/mlx5e: Receive buffer configuration")
Signed-off-by: NHuy Nguyen <huyn@mellanox.com>
Signed-off-by: NSaeed Mahameed <saeedm@mellanox.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>

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

@@ -143,7 +143,7 @@ static u32 calculate_xoff(struct mlx5e_priv *priv, unsigned int mtu)
 }
 
 static int update_xoff_threshold(struct mlx5e_port_buffer *port_buffer,
-				 u32 xoff, unsigned int mtu)
+				 u32 xoff, unsigned int max_mtu)
 {
 	int i;
 
@@ -155,11 +155,12 @@ static int update_xoff_threshold(struct mlx5e_port_buffer *port_buffer,
 		}
 
 		if (port_buffer->buffer[i].size <
-		    (xoff + mtu + (1 << MLX5E_BUFFER_CELL_SHIFT)))
+		    (xoff + max_mtu + (1 << MLX5E_BUFFER_CELL_SHIFT)))
 			return -ENOMEM;
 
 		port_buffer->buffer[i].xoff = port_buffer->buffer[i].size - xoff;
-		port_buffer->buffer[i].xon  = port_buffer->buffer[i].xoff - mtu;
+		port_buffer->buffer[i].xon  =
+			port_buffer->buffer[i].xoff - max_mtu;
 	}
 
 	return 0;
@@ -167,7 +168,7 @@ static int update_xoff_threshold(struct mlx5e_port_buffer *port_buffer,
 
 /**
  * update_buffer_lossy()
- *   mtu: device's MTU
+ *   max_mtu: netdev's max_mtu
  *   pfc_en: <input> current pfc configuration
  *   buffer: <input> current prio to buffer mapping
  *   xoff:   <input> xoff value
@@ -184,7 +185,7 @@ static int update_xoff_threshold(struct mlx5e_port_buffer *port_buffer,
  *     Return 0 if no error.
  *     Set change to true if buffer configuration is modified.
  */
-static int update_buffer_lossy(unsigned int mtu,
+static int update_buffer_lossy(unsigned int max_mtu,
 			       u8 pfc_en, u8 *buffer, u32 xoff,
 			       struct mlx5e_port_buffer *port_buffer,
 			       bool *change)
@@ -221,7 +222,7 @@ static int update_buffer_lossy(unsigned int mtu,
 	}
 
 	if (changed) {
-		err = update_xoff_threshold(port_buffer, xoff, mtu);
+		err = update_xoff_threshold(port_buffer, xoff, max_mtu);
 		if (err)
 			return err;
 
@@ -231,6 +232,7 @@ static int update_buffer_lossy(unsigned int mtu,
 	return 0;
 }
 
+#define MINIMUM_MAX_MTU 9216
 int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 				    u32 change, unsigned int mtu,
 				    struct ieee_pfc *pfc,
@@ -242,12 +244,14 @@ int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 	bool update_prio2buffer = false;
 	u8 buffer[MLX5E_MAX_PRIORITY];
 	bool update_buffer = false;
+	unsigned int max_mtu;
 	u32 total_used = 0;
 	u8 curr_pfc_en;
 	int err;
 	int i;
 
 	mlx5e_dbg(HW, priv, "%s: change=%x\n", __func__, change);
+	max_mtu = max_t(unsigned int, priv->netdev->max_mtu, MINIMUM_MAX_MTU);
 
 	err = mlx5e_port_query_buffer(priv, &port_buffer);
 	if (err)
@@ -255,7 +259,7 @@ int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 
 	if (change & MLX5E_PORT_BUFFER_CABLE_LEN) {
 		update_buffer = true;
-		err = update_xoff_threshold(&port_buffer, xoff, mtu);
+		err = update_xoff_threshold(&port_buffer, xoff, max_mtu);
 		if (err)
 			return err;
 	}
@@ -265,7 +269,7 @@ int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 		if (err)
 			return err;
 
-		err = update_buffer_lossy(mtu, pfc->pfc_en, buffer, xoff,
+		err = update_buffer_lossy(max_mtu, pfc->pfc_en, buffer, xoff,
 					  &port_buffer, &update_buffer);
 		if (err)
 			return err;
@@ -277,8 +281,8 @@ int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 		if (err)
 			return err;
 
-		err = update_buffer_lossy(mtu, curr_pfc_en, prio2buffer, xoff,
-					  &port_buffer, &update_buffer);
+		err = update_buffer_lossy(max_mtu, curr_pfc_en, prio2buffer,
+					  xoff, &port_buffer, &update_buffer);
 		if (err)
 			return err;
 	}
@@ -302,7 +306,7 @@ int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 			return -EINVAL;
 
 		update_buffer = true;
-		err = update_xoff_threshold(&port_buffer, xoff, mtu);
+		err = update_xoff_threshold(&port_buffer, xoff, max_mtu);
 		if (err)
 			return err;
 	}
@@ -310,7 +314,7 @@ int mlx5e_port_manual_buffer_config(struct mlx5e_priv *priv,
 	/* Need to update buffer configuration if xoff value is changed */
 	if (!update_buffer && xoff != priv->dcbx.xoff) {
 		update_buffer = true;
-		err = update_xoff_threshold(&port_buffer, xoff, mtu);
+		err = update_xoff_threshold(&port_buffer, xoff, max_mtu);
 		if (err)
 			return err;
 	}