net: ena: Eliminate duplicate barriers on weakly-ordered archs

Code includes barrier() followed by writel(). writel() already has a
barrier on some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the
register write.

Create a new wrapper function with relaxed write operator. Use the new
wrapper when a write is following a barrier().

Since code already has an explicit barrier call, changing writel() to
writel_relaxed() and adding mmiowb() for ordering protection.

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
index bf2de5298005d0ea63ce0d9690d1786722881937..1b9d3130af4d64f844498d19b93adf8da0f2ebc6 100644 (file)
--- a/drivers/net/ethernet/amazon/ena/ena_com.c
+++ b/drivers/net/ethernet/amazon/ena/ena_com.c
@@ -631,8 +631,10 @@ static u32 ena_com_reg_bar_read32(struct ena_com_dev *ena_dev, u16 offset)
         */
        wmb();
 
-       writel(mmio_read_reg, ena_dev->reg_bar + ENA_REGS_MMIO_REG_READ_OFF);
+       writel_relaxed(mmio_read_reg,
+                      ena_dev->reg_bar + ENA_REGS_MMIO_REG_READ_OFF);
 
+       mmiowb();
        for (i = 0; i < timeout; i++) {
                if (read_resp->req_id == mmio_read->seq_num)
                        break;
@@ -1826,7 +1828,9 @@ void ena_com_aenq_intr_handler(struct ena_com_dev *dev, void *data)
 
        /* write the aenq doorbell after all AENQ descriptors were read */
        mb();
-       writel((u32)aenq->head, dev->reg_bar + ENA_REGS_AENQ_HEAD_DB_OFF);
+       writel_relaxed((u32)aenq->head,
+                      dev->reg_bar + ENA_REGS_AENQ_HEAD_DB_OFF);
+       mmiowb();
 }
 
 int ena_com_dev_reset(struct ena_com_dev *ena_dev,

diff --git a/drivers/net/ethernet/amazon/ena/ena_eth_com.h b/drivers/net/ethernet/amazon/ena/ena_eth_com.h
index 2f7657227cfe9c60d77482c98df22fdb2f89e3c9..6fdc753d948382e7a56aaeac801cf16ab3b8f833 100644 (file)
--- a/drivers/net/ethernet/amazon/ena/ena_eth_com.h
+++ b/drivers/net/ethernet/amazon/ena/ena_eth_com.h
@@ -107,7 +107,8 @@ static inline int ena_com_sq_empty_space(struct ena_com_io_sq *io_sq)
        return io_sq->q_depth - 1 - cnt;
 }
 
-static inline int ena_com_write_sq_doorbell(struct ena_com_io_sq *io_sq)
+static inline int ena_com_write_sq_doorbell(struct ena_com_io_sq *io_sq,
+                                           bool relaxed)
 {
        u16 tail;
 
@@ -116,7 +117,10 @@ static inline int ena_com_write_sq_doorbell(struct ena_com_io_sq *io_sq)
        pr_debug("write submission queue doorbell for queue: %d tail: %d\n",
                 io_sq->qid, tail);
 
-       writel(tail, io_sq->db_addr);
+       if (relaxed)
+               writel_relaxed(tail, io_sq->db_addr);
+       else
+               writel(tail, io_sq->db_addr);
 
        return 0;
 }

diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
index 6975150d144e5ec8726d30cfe888b6888bb7a8b4..a822e70c2af35a650a8c524c5820f64561044454 100644 (file)
--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
@@ -556,7 +556,8 @@ static int ena_refill_rx_bufs(struct ena_ring *rx_ring, u32 num)
                 * issue a doorbell
                 */
                wmb();
-               ena_com_write_sq_doorbell(rx_ring->ena_com_io_sq);
+               ena_com_write_sq_doorbell(rx_ring->ena_com_io_sq, true);
+               mmiowb();
        }
 
        rx_ring->next_to_use = next_to_use;
@@ -2151,7 +2152,7 @@ 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);
+               ena_com_write_sq_doorbell(tx_ring->ena_com_io_sq, false);
                u64_stats_update_begin(&tx_ring->syncp);
                tx_ring->tx_stats.doorbells++;
                u64_stats_update_end(&tx_ring->syncp);