linux-kernel - [PATCH net v3] octeon_ep: update BQL sent bytes before ringing doorbell

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Date:   Tue, 17 Oct 2023 03:50:30 -0700
From:   Shinas Rasheed <srasheed@...vell.com>
To:     <kuba@...nel.org>, <linux-kernel@...r.kernel.org>
CC:     <pabeni@...hat.com>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <egallen@...hat.com>, <hgani@...vell.com>, <mschmidt@...hat.com>,
        <netdev@...r.kernel.org>, <srasheed@...vell.com>,
        <sedara@...vell.com>, <vburru@...vell.com>, <vimleshk@...vell.com>
Subject: [PATCH net v3] octeon_ep: update BQL sent bytes before ringing doorbell

Sometimes Tx is completed immediately after doorbell is updated, which
causes Tx completion routing to update completion bytes before the
same packet bytes are updated in sent bytes in transmit function, hence
hitting BUG_ON() in dql_completed(). To avoid this, update BQL
sent bytes before ringing doorbell.

Fixes: 37d79d059606 ("octeon_ep: add Tx/Rx processing and interrupt support")
Signed-off-by: Shinas Rasheed <srasheed@...vell.com>
---
V3:
  - Update skb timestamp and host write index before memory barrier
V2: https://lore.kernel.org/all/20231012101706.2291551-1-srasheed@marvell.com/
  - Call netdev_tx_sent_queue before memory barrier
V1: https://lore.kernel.org/all/20231010115015.2279977-1-srasheed@marvell.com/

 drivers/net/ethernet/marvell/octeon_ep/octep_main.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/marvell/octeon_ep/octep_main.c b/drivers/net/ethernet/marvell/octeon_ep/octep_main.c
index dbc518ff8276..5b46ca47c8e5 100644
--- a/drivers/net/ethernet/marvell/octeon_ep/octep_main.c
+++ b/drivers/net/ethernet/marvell/octeon_ep/octep_main.c
@@ -715,20 +715,19 @@ static netdev_tx_t octep_start_xmit(struct sk_buff *skb,
 		hw_desc->dptr = tx_buffer->sglist_dma;
 	}
 
-	/* Flush the hw descriptor before writing to doorbell */
-	wmb();
-
-	/* Ring Doorbell to notify the NIC there is a new packet */
-	writel(1, iq->doorbell_reg);
+	netdev_tx_sent_queue(iq->netdev_q, skb->len);
+	skb_tx_timestamp(skb);
 	atomic_inc(&iq->instr_pending);
 	wi++;
 	if (wi == iq->max_count)
 		wi = 0;
 	iq->host_write_index = wi;
+	/* Flush the hw descriptor before writing to doorbell */
+	wmb();
 
-	netdev_tx_sent_queue(iq->netdev_q, skb->len);
+	/* Ring Doorbell to notify the NIC there is a new packet */
+	writel(1, iq->doorbell_reg);
 	iq->stats.instr_posted++;
-	skb_tx_timestamp(skb);
 	return NETDEV_TX_OK;
 
 dma_map_sg_err:
-- 
2.25.1