mlxsw: spectrum_buffers: Prevent changing CPU port's configuration

Next patch is going to register the CPU port with devlink, but only so
that the CPU port's shared buffer configuration and occupancy could be
queried.

Prevent changing CPU port's shared buffer threshold and binding
configuration.
Signed-off-by: NShalom Toledo <shalomt@mellanox.com>
Acked-by: NJiri Pirko <jiri@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_buffers.c

@@ -1085,6 +1085,11 @@ int mlxsw_sp_sb_port_pool_set(struct mlxsw_core_port *mlxsw_core_port,
 	u32 max_buff;
 	int err;
 
+	if (local_port == MLXSW_PORT_CPU_PORT) {
+		NL_SET_ERR_MSG_MOD(extack, "Changing CPU port's threshold is forbidden");
+		return -EINVAL;
+	}
+
 	err = mlxsw_sp_sb_threshold_in(mlxsw_sp, pool_index,
 				       threshold, &max_buff, extack);
 	if (err)
@@ -1130,6 +1135,11 @@ int mlxsw_sp_sb_tc_pool_bind_set(struct mlxsw_core_port *mlxsw_core_port,
 	u32 max_buff;
 	int err;
 
+	if (local_port == MLXSW_PORT_CPU_PORT) {
+		NL_SET_ERR_MSG_MOD(extack, "Changing CPU port's binding is forbidden");
+		return -EINVAL;
+	}
+
 	if (dir != mlxsw_sp->sb_vals->pool_dess[pool_index].dir) {
 		NL_SET_ERR_MSG_MOD(extack, "Binding egress TC to ingress pool and vice versa is forbidden");
 		return -EINVAL;