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Commit 6d2e1a8d authored by Sinan Kaya's avatar Sinan Kaya Committed by David S. Miller
Browse files

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: default avatarSinan Kaya <okaya@codeaurora.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fd141fa4

drivers/net/ethernet/amazon/ena/ena_com.c

+6 −2
Original line number Diff line number Diff line
@@ -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,

drivers/net/ethernet/amazon/ena/ena_eth_com.h

+6 −2
Original line number Diff line number Diff line
@@ -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;
@@ -116,6 +117,9 @@ 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);



	if (relaxed)

		writel_relaxed(tail, io_sq->db_addr);

	else

		writel(tail, io_sq->db_addr);



	return 0;

drivers/net/ethernet/amazon/ena/ena_netdev.c

+3 −2
Original line number Diff line number Diff line
@@ -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);