[dpdk-dev] [PATCH RFC v1 2/7] net/ena: relax the barrier for doorbell ring

[Gavin Hu]

rte_cio_wmb is a light weight version of IO memory barrier that
guarantees that the stores to the coherent memory prior to the
the rte_cio_rmb() call are visible to the NIC HW before the doorbell
ring(or any other stores to the MMIO registers) that follows it.[1]

Fixes: 5e02e19eb14e ("net/ena: fix unneeded doorbell submission")
Cc: stable at dpdk.org

[1] http://code.dpdk.org/dpdk/v20.02/source/lib/librte_eal/common/
include/generic/rte_atomic.h#L137

Signed-off-by: Gavin Hu <gavin.hu at arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
---
 drivers/net/ena/ena_ethdev.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ena/ena_ethdev.c b/drivers/net/ena/ena_ethdev.c
index 665afee4f..c268788fd 100644
--- a/drivers/net/ena/ena_ethdev.c
+++ b/drivers/net/ena/ena_ethdev.c
@@ -1425,7 +1425,7 @@ static int ena_populate_rx_queue(struct ena_ring *rxq, unsigned int count)
 		 * Add memory barrier to make sure the desc were written before
 		 * issue a doorbell
 		 */
-		rte_wmb();
+		rte_cio_wmb();
 		ena_com_write_sq_doorbell(rxq->ena_com_io_sq);
 
 		rxq->next_to_use = next_to_use;
@@ -2344,7 +2344,7 @@ static uint16_t eth_ena_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 			PMD_DRV_LOG(DEBUG, "llq tx max burst size of queue %d"
 				" achieved, writing doorbell to send burst\n",
 				tx_ring->id);
-			rte_wmb();
+			rte_cio_wmb();
 			ena_com_write_sq_doorbell(tx_ring->ena_com_io_sq);
 		}
 
@@ -2367,7 +2367,7 @@ static uint16_t eth_ena_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 	/* If there are ready packets to be xmitted... */
 	if (sent_idx > 0) {
 		/* ...let HW do its best :-) */
-		rte_wmb();
+		rte_cio_wmb();
 		ena_com_write_sq_doorbell(tx_ring->ena_com_io_sq);
 		tx_ring->tx_stats.doorbells++;
 		tx_ring->next_to_use = next_to_use;
-- 
2.17.1