[PATCH v7 5/7] net: qlge: Eliminate duplicate barriers on weakly-ordered archs

Sinan Kaya
2018-03-25T14:41:33Z

Code includes wmb() 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 wmb().

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
---
drivers/net/ethernet/qlogic/qlge/qlge.h | 16 ++++++++++++++++
drivers/net/ethernet/qlogic/qlge/qlge_main.c | 3 ++-
2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/qlogic/qlge/qlge.h b/drivers/net/ethernet/qlogic/qlge/qlge.h
index 84ac50f..3e71b65 100644
--- a/drivers/net/ethernet/qlogic/qlge/qlge.h
+++ b/drivers/net/ethernet/qlogic/qlge/qlge.h
@@ -2185,6 +2185,22 @@ static inline void ql_write_db_reg(u32 val, void __iomem *addr)
}

/*
+ * Doorbell Registers:
+ * Doorbell registers are virtual registers in the PCI memory space.
+ * The space is allocated by the chip during PCI initialization. The
+ * device driver finds the doorbell address in BAR 3 in PCI config space.
+ * The registers are used to control outbound and inbound queues. For
+ * example, the producer index for an outbound queue. Each queue uses
+ * 1 4k chunk of memory. The lower half of the space is for outbound
+ * queues. The upper half is for inbound queues.
+ * Caller has to guarantee ordering.
+ */
+static inline void ql_write_db_reg_relaxed(u32 val, void __iomem *addr)
+{
+ writel_relaxed(val, addr);
+}
+
+/*
* Shadow Registers:
* Outbound queues have a consumer index that is maintained by the chip.
* Inbound queues have a producer index that is maintained by the chip.
diff --git a/drivers/net/ethernet/qlogic/qlge/qlge_main.c b/drivers/net/ethernet/qlogic/qlge/qlge_main.c
index 50038d9..8293c202 100644
--- a/drivers/net/ethernet/qlogic/qlge/qlge_main.c
+++ b/drivers/net/ethernet/qlogic/qlge/qlge_main.c
@@ -2700,7 +2700,8 @@ static netdev_tx_t qlge_send(struct sk_buff *skb, struct net_device *ndev)
tx_ring->prod_idx = 0;
wmb();

- ql_write_db_reg(tx_ring->prod_idx, tx_ring->prod_idx_db_reg);
+ ql_write_db_reg_relaxed(tx_ring->prod_idx, tx_ring->prod_idx_db_reg);
+ mmiowb();
netif_printk(qdev, tx_queued, KERN_DEBUG, qdev->ndev,
"tx queued, slot %d, len %d\n",
tx_ring->prod_idx, skb->len);
--
2.7.4