net: ena: fix incorrect usage of memory barriers

Added memory barriers where they were missing to support multiple
architectures, and removed redundant ones.

As part of removing the redundant memory barriers and improving
performance, we moved to more relaxed versions of memory barriers,
as well as to the more relaxed version of writel - writel_relaxed,
while maintaining correctness.

Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 19 deletions

diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
index b9ce2a6a87ed..29b5774dd32d 100644
--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
@@ -551,14 +551,9 @@ static int ena_refill_rx_bufs(struct ena_ring *rx_ring, u32 num)
 			    rx_ring->qid, i, num);
 	}
 
-	if (likely(i)) {
-		/* Add memory barrier to make sure the desc were written before
-		 * issue a doorbell
-		 */
-		wmb();
-		ena_com_write_sq_doorbell(rx_ring->ena_com_io_sq, true);
-		mmiowb();
-	}
+	/* ena_com_write_sq_doorbell issues a wmb() */
+	if (likely(i))
+		ena_com_write_sq_doorbell(rx_ring->ena_com_io_sq);
 
 	rx_ring->next_to_use = next_to_use;
 
@@ -2112,12 +2107,6 @@ static netdev_tx_t ena_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	tx_ring->next_to_use = ENA_TX_RING_IDX_NEXT(next_to_use,
 		tx_ring->ring_size);
 
-	/* This WMB is aimed to:
-	 * 1 - perform smp barrier before reading next_to_completion
-	 * 2 - make sure the desc were written before trigger DB
-	 */
-	wmb();
-
 	/* stop the queue when no more space available, the packet can have up
 	 * to sgl_size + 2. one for the meta descriptor and one for header
 	 * (if the header is larger than tx_max_header_size).
@@ -2136,10 +2125,11 @@ static netdev_tx_t ena_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		 * stop the queue but meanwhile clean_tx_irq updates
 		 * next_to_completion and terminates.
 		 * The queue will remain stopped forever.
-		 * To solve this issue this function perform rmb, check
-		 * the wakeup condition and wake up the queue if needed.
+		 * To solve this issue add a mb() to make sure that
+		 * netif_tx_stop_queue() write is vissible before checking if
+		 * there is additional space in the queue.
 		 */
-		smp_rmb();
+		smp_mb();
 
 		if (ena_com_sq_empty_space(tx_ring->ena_com_io_sq)
 				> ENA_TX_WAKEUP_THRESH) {
@@ -2151,8 +2141,10 @@ static netdev_tx_t ena_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 
 	if (netif_xmit_stopped(txq) || !skb->xmit_more) {
-		/* trigger the dma engine */
-		ena_com_write_sq_doorbell(tx_ring->ena_com_io_sq, false);
+		/* trigger the dma engine. ena_com_write_sq_doorbell()
+		 * has a mb
+		 */
+		ena_com_write_sq_doorbell(tx_ring->ena_com_io_sq);
 		u64_stats_update_begin(&tx_ring->syncp);
 		tx_ring->tx_stats.doorbells++;
 		u64_stats_update_end(&tx_ring->syncp);