netdev - [PATCH V2 net-next 5/6] net: hns3: use writel() to optimize the barrier operation

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Date:   Wed, 16 Sep 2020 17:33:49 +0800
From:   Huazhong Tan <tanhuazhong@...wei.com>
To:     <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <salil.mehta@...wei.com>, <yisen.zhuang@...wei.com>,
        <linuxarm@...wei.com>, <kuba@...nel.org>, <saeed@...nel.org>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Huazhong Tan <tanhuazhong@...wei.com>
Subject: [PATCH V2 net-next 5/6] net: hns3: use writel() to optimize the barrier operation

From: Yunsheng Lin <linyunsheng@...wei.com>

writel() can be used to order I/O vs memory by default when
writing portable drivers. Use writel() to replace wmb() +
writel_relaxed(), and writel() is dma_wmb() + writel_relaxed()
for ARM64, so there is an optimization here because dma_wmb()
is a lighter barrier than wmb().

Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>
---
 drivers/net/ethernet/hisilicon/hns3/hns3_enet.c | 8 +++-----
 drivers/net/ethernet/hisilicon/hns3/hns3_enet.h | 3 ---
 2 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
index 8490754..4a49a76 100644
--- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
+++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
@@ -1398,9 +1398,8 @@ static void hns3_tx_doorbell(struct hns3_enet_ring *ring, int num,
 	if (!ring->pending_buf)
 		return;
 
-	wmb(); /* Commit all data before submit */
-
-	hnae3_queue_xmit(ring->tqp, ring->pending_buf);
+	writel(ring->pending_buf,
+	       ring->tqp->io_base + HNS3_RING_TX_RING_TAIL_REG);
 	ring->pending_buf = 0;
 	WRITE_ONCE(ring->last_to_use, ring->next_to_use);
 }
@@ -2618,8 +2617,7 @@ static void hns3_nic_alloc_rx_buffers(struct hns3_enet_ring *ring,
 		ring_ptr_move_fw(ring, next_to_use);
 	}
 
-	wmb(); /* Make all data has been write before submit */
-	writel_relaxed(i, ring->tqp->io_base + HNS3_RING_RX_RING_HEAD_REG);
+	writel(i, ring->tqp->io_base + HNS3_RING_RX_RING_HEAD_REG);
 }
 
 static bool hns3_page_is_reusable(struct page *page)
diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h
index 876dc09..20e62ce 100644
--- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h
+++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h
@@ -539,9 +539,6 @@ static inline bool hns3_nic_resetting(struct net_device *netdev)
 #define hns3_write_dev(a, reg, value) \
 	hns3_write_reg((a)->io_base, (reg), (value))
 
-#define hnae3_queue_xmit(tqp, buf_num) writel_relaxed(buf_num, \
-		(tqp)->io_base + HNS3_RING_TX_RING_TAIL_REG)
-
 #define ring_to_dev(ring) ((ring)->dev)
 
 #define ring_to_netdev(ring)	((ring)->tqp_vector->napi.dev)
-- 
2.7.4