[dpdk-dev] MLX5 driver - number of descriptors overflow

[Amedeo Sapio <amedeo.sapio@gmail.com>]

Hello,

I experienced a problem with the MLX5 driver running a code that is working
fine with an Intel card. I have found that the reason of this error is an
overflow of the uint16_t number of descriptors in the mlx driver.

Here the details:

- The NIC is a Mellanox ConnectX-5 100G.

- This is a summary code that I run to initialize the port:

        ret = rte_eth_dev_configure(dpdk_par.portid, 1, 1, &port_conf);

        dpdk_par.port_rx_ring_size = dev_info.rx_desc_lim.nb_max;
        dpdk_par.port_tx_ring_size = dev_info.tx_desc_lim.nb_max;

        ret = rte_eth_dev_adjust_nb_rx_tx_desc(dpdk_par.portid,
&dpdk_par.port_rx_ring_size, &dpdk_par.port_tx_ring_size);

        ret = rte_eth_rx_queue_setup(dpdk_par.portid, 0,
dpdk_par.port_rx_ring_size, rte_eth_dev_socket_id(dpdk_par.portid),
&rx_conf, dpdk_data.pool);
        ret = rte_eth_tx_queue_setup(dpdk_par.portid, 0,
dpdk_par.port_tx_ring_size, rte_eth_dev_socket_id(dpdk_par.portid),
&tx_conf);

        ret = rte_eth_dev_start(dpdk_par.portid);

- The "rte_eth_dev_start" function returns  -ENOMEM  =  -12 (Out of memory)

- I see that "dev_info.rx_desc_lim.nb_max" is 65535.  This value is rounded
to the next power of 2 in "mlx5_rx_queue_setup",  which overflows and
becomes 0.

I thought that  "rte_eth_dev_adjust_nb_rx_tx_desc" should have adjusted the
value, but clearly it has not.

Thanks,
---
Amedeo