net: Google gve: Remove dma_wmb() before ringing doorbell

Current code use dma_wmb() to ensure Rx/Tx descriptors are visible
to device before writing to doorbell.

However, these dma_wmb() are wrong and unnecessary. Therefore,
they should be removed.

iowrite32be() called from gve_rx_write_doorbell()/gve_tx_put_doorbell()
should guaratee that all previous writes to WB/UC memory is visible to
device before the write done by iowrite32be().

E.g. On ARM64, iowrite32be() calls __iowmb() which expands to dma_wmb()
and only then calls __raw_writel().

Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/google/gve/gve_rx.c b/drivers/net/ethernet/google/gve/gve_rx.c
index edec61d..9f52e72 100644 (file)
--- a/drivers/net/ethernet/google/gve/gve_rx.c
+++ b/drivers/net/ethernet/google/gve/gve_rx.c
@@ -418,8 +418,6 @@ bool gve_clean_rx_done(struct gve_rx_ring *rx, int budget,
        rx->cnt = cnt;
        rx->fill_cnt += work_done;
 
-       /* restock desc ring slots */
-       dma_wmb();      /* Ensure descs are visible before ringing doorbell */
        gve_rx_write_doorbell(priv, rx);
        return gve_rx_work_pending(rx);
 }

diff --git a/drivers/net/ethernet/google/gve/gve_tx.c b/drivers/net/ethernet/google/gve/gve_tx.c
index f488943..d0244fe 100644 (file)
--- a/drivers/net/ethernet/google/gve/gve_tx.c
+++ b/drivers/net/ethernet/google/gve/gve_tx.c
@@ -487,10 +487,6 @@ netdev_tx_t gve_tx(struct sk_buff *skb, struct net_device *dev)
                 * may have added descriptors without ringing the doorbell.
                 */
 
-               /* Ensure tx descs from a prior gve_tx are visible before
-                * ringing doorbell.
-                */
-               dma_wmb();
                gve_tx_put_doorbell(priv, tx->q_resources, tx->req);
                return NETDEV_TX_BUSY;
        }
@@ -505,8 +501,6 @@ netdev_tx_t gve_tx(struct sk_buff *skb, struct net_device *dev)
        if (!netif_xmit_stopped(tx->netdev_txq) && netdev_xmit_more())
                return NETDEV_TX_OK;
 
-       /* Ensure tx descs are visible before ringing doorbell */
-       dma_wmb();
        gve_tx_put_doorbell(priv, tx->q_resources, tx->req);
        return NETDEV_TX_OK;
 }