[dpdk-dev] [PATCH] net/mlx5: fix minimum size of Multi-Packet Rx queue

[Yongseok Koh <yskoh@mellanox.com>]

The size of Rx queue is determined by dividing the number of descriptors by
the number of strides. As device can't support single slot queue, if the
number of descriptors is same as the number of strides, MPRQ shouldn't be
enabled. Otherwise, this will cause HW fault. For example, if rxd is set to
512 with testpmd on ConnectX-4 Lx, PMD can't receive more than 512 packets
because the minimum number of strides for ConnectX-4 Lx is 512. Users have
to configure larger number of descriptors in this case.

Fixes: 7d6bf6b866b8 ("net/mlx5: add Multi-Packet Rx support")
Cc: stable@dpdk.org

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
---
 drivers/net/mlx5/mlx5_rxq.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
index 8b4c1b1a14..1f7bfd4414 100644
--- a/drivers/net/mlx5/mlx5_rxq.c
+++ b/drivers/net/mlx5/mlx5_rxq.c
@@ -1356,7 +1356,7 @@ mlx5_rxq_new(struct rte_eth_dev *dev, uint16_t idx, uint16_t desc,
 		sizeof(struct rte_mbuf_ext_shared_info) +
 		RTE_PKTMBUF_HEADROOM;
 	if (mprq_en &&
-	    desc >= (1U << config->mprq.stride_num_n) &&
+	    desc > (1U << config->mprq.stride_num_n) &&
 	    mprq_stride_size <= (1U << config->mprq.max_stride_size_n)) {
 		/* TODO: Rx scatter isn't supported yet. */
 		tmpl->rxq.sges_n = 0;
@@ -1411,6 +1411,14 @@ mlx5_rxq_new(struct rte_eth_dev *dev, uint16_t idx, uint16_t desc,
 			dev->data->dev_conf.rxmode.max_rx_pkt_len,
 			mb_len - RTE_PKTMBUF_HEADROOM);
 	}
+	if (mprq_en && !mlx5_rxq_mprq_enabled(&tmpl->rxq))
+		DRV_LOG(WARNING,
+			"port %u MPRQ is requested but cannot be enabled"
+			" (requested: desc = %u, stride_sz = %u,"
+			" supported: min_stride_num = %u, max_stride_sz = %u).",
+			dev->data->port_id, desc, mprq_stride_size,
+			(1 << config->mprq.stride_num_n),
+			(1 << config->mprq.max_stride_size_n));
 	DRV_LOG(DEBUG, "port %u maximum number of segments per packet: %u",
 		dev->data->port_id, 1 << tmpl->rxq.sges_n);
 	if (desc % (1 << tmpl->rxq.sges_n)) {
-- 
2.11.0