[PATCH 5.4 066/110] net: Google gve: Remove dma_wmb() before ringing doorbell

Greg Kroah-Hartman
2020-01-30T18:44:34Z

From: Liran Alon <liran.alon@oracle.com>

[ Upstream commit b54ef37b1ce892fdf6b632d566246d2f2f539910 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/google/gve/gve_rx.c | 2 --
drivers/net/ethernet/google/gve/gve_tx.c | 6 ------
2 files changed, 8 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_rx.c b/drivers/net/ethernet/google/gve/gve_rx.c
index edec61dfc8687..9f52e72ff641d 100644
--- 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 f4889431f9b70..d0244feb03011 100644
--- 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;
}
--
2.20.1