netdev - [PATCH net-next 2/3] bnxt: use READ_ONCE/WRITE

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Message-Id: <20230411013323.513688-3-kuba@kernel.org>
Date:   Mon, 10 Apr 2023 18:33:22 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
        Jakub Kicinski <kuba@...nel.org>, michael.chan@...adcom.com
Subject: [PATCH net-next 2/3] bnxt: use READ_ONCE/WRITE_ONCE for ring indexes

Eric points out that we should make sure that ring index updates
are wrapped in the appropriate READ_ONCE/WRITE_ONCE macros.

Suggested-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
CC: michael.chan@...adcom.com
---
 drivers/net/ethernet/broadcom/bnxt/bnxt.c | 6 +++---
 drivers/net/ethernet/broadcom/bnxt/bnxt.h | 9 ++++-----
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
index f7602d8d79e3..92289ab2f34a 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
@@ -472,7 +472,7 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		prod = NEXT_TX(prod);
 		tx_push->doorbell =
 			cpu_to_le32(DB_KEY_TX_PUSH | DB_LONG_TX_PUSH | prod);
-		txr->tx_prod = prod;
+		WRITE_ONCE(txr->tx_prod, prod);
 
 		tx_buf->is_push = 1;
 		netdev_tx_sent_queue(txq, skb->len);
@@ -583,7 +583,7 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	wmb();
 
 	prod = NEXT_TX(prod);
-	txr->tx_prod = prod;
+	WRITE_ONCE(txr->tx_prod, prod);
 
 	if (!netdev_xmit_more() || netif_xmit_stopped(txq))
 		bnxt_txr_db_kick(bp, txr, prod);
@@ -688,7 +688,7 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 		dev_kfree_skb_any(skb);
 	}
 
-	txr->tx_cons = cons;
+	WRITE_ONCE(txr->tx_cons, cons);
 
 	__netif_txq_completed_wake(txq, nr_pkts, tx_bytes,
 				   bnxt_tx_avail(bp, txr), bp->tx_wake_thresh,
diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.h b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
index 18cac98ba58e..080e73496066 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.h
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
@@ -2231,13 +2231,12 @@ struct bnxt {
 #define SFF_MODULE_ID_QSFP28			0x11
 #define BNXT_MAX_PHY_I2C_RESP_SIZE		64
 
-static inline u32 bnxt_tx_avail(struct bnxt *bp, struct bnxt_tx_ring_info *txr)
+static inline u32 bnxt_tx_avail(struct bnxt *bp,
+				const struct bnxt_tx_ring_info *txr)
 {
-	/* Tell compiler to fetch tx indices from memory. */
-	barrier();
+	u32 used = READ_ONCE(txr->tx_prod) - READ_ONCE(txr->tx_cons);
 
-	return bp->tx_ring_size -
-		((txr->tx_prod - txr->tx_cons) & bp->tx_ring_mask);
+	return bp->tx_ring_size - (used & bp->tx_ring_mask);
 }
 
 static inline void bnxt_writeq(struct bnxt *bp, u64 val,
-- 
2.39.2