linux-kernel - [PATCH] net: ftgmac100: Ensure tx descriptor updates are visible

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Message-Id: <20201020220639.130696-1-joel@jms.id.au>
Date:   Wed, 21 Oct 2020 08:36:39 +1030
From:   Joel Stanley <joel@....id.au>
To:     Jakub Kicinski <kuba@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Dylan Hung <dylan_hung@...eedtech.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-aspeed@...ts.ozlabs.org
Subject: [PATCH] net: ftgmac100: Ensure tx descriptor updates are visible

We must ensure the tx descriptor updates are visible before updating
the tx pointer.

This resolves the tx hangs observed on the 2600 when running iperf:

root@...2600:~# iperf3 -c 192.168.86.146 -R
Connecting to host 192.168.86.146, port 5201
Reverse mode, remote host 192.168.86.146 is sending
[  5] local 192.168.86.173 port 43886 connected to 192.168.86.146 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  90.7 MBytes   760 Mbits/sec
[  5]   1.00-2.00   sec  91.7 MBytes   769 Mbits/sec
[  5]   2.00-3.00   sec  91.7 MBytes   770 Mbits/sec
[  5]   3.00-4.00   sec  91.7 MBytes   769 Mbits/sec
[  5]   4.00-5.00   sec  91.8 MBytes   771 Mbits/sec
[  5]   5.00-6.00   sec  91.8 MBytes   771 Mbits/sec
[  5]   6.00-7.00   sec  91.9 MBytes   771 Mbits/sec
[  5]   7.00-8.00   sec  91.4 MBytes   767 Mbits/sec
[  5]   8.00-9.00   sec  91.3 MBytes   766 Mbits/sec
[  5]   9.00-10.00  sec  91.9 MBytes   771 Mbits/sec
[  5]  10.00-11.00  sec  91.8 MBytes   770 Mbits/sec
[  5]  11.00-12.00  sec  91.8 MBytes   770 Mbits/sec
[  5]  12.00-13.00  sec  90.6 MBytes   761 Mbits/sec
[  5]  13.00-14.00  sec  45.2 KBytes   370 Kbits/sec
[  5]  14.00-15.00  sec  0.00 Bytes  0.00 bits/sec
[  5]  15.00-16.00  sec  0.00 Bytes  0.00 bits/sec
[  5]  16.00-17.00  sec  0.00 Bytes  0.00 bits/sec
[  5]  17.00-18.00  sec  0.00 Bytes  0.00 bits/sec
[   67.031671] ------------[ cut here ]------------
[   67.036870] WARNING: CPU: 1 PID: 0 at net/sched/sch_generic.c:442 dev_watchdog+0x2dc/0x300
[   67.046123] NETDEV WATCHDOG: eth2 (ftgmac100): transmit queue 0 timed out

Fixes: 52c0cae87465 ("ftgmac100: Remove tx descriptor accessors")
Signed-off-by: Joel Stanley <joel@....id.au>
---
 drivers/net/ethernet/faraday/ftgmac100.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
index 331d4bdd4a67..15cdfeb135b0 100644
--- a/drivers/net/ethernet/faraday/ftgmac100.c
+++ b/drivers/net/ethernet/faraday/ftgmac100.c
@@ -653,6 +653,11 @@ static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv)
 	ftgmac100_free_tx_packet(priv, pointer, skb, txdes, ctl_stat);
 	txdes->txdes0 = cpu_to_le32(ctl_stat & priv->txdes0_edotr_mask);
 
+	/* Ensure the descriptor config is visible before setting the tx
+	 * pointer.
+	 */
+	smp_wmb();
+
 	priv->tx_clean_pointer = ftgmac100_next_tx_pointer(priv, pointer);
 
 	return true;
@@ -806,6 +811,11 @@ static netdev_tx_t ftgmac100_hard_start_xmit(struct sk_buff *skb,
 	dma_wmb();
 	first->txdes0 = cpu_to_le32(f_ctl_stat);
 
+	/* Ensure the descriptor config is visible before setting the tx
+	 * pointer.
+	 */
+	smp_wmb();
+
 	/* Update next TX pointer */
 	priv->tx_pointer = pointer;
 
-- 
2.28.0