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

[Joel Stanley]

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@ast2600:~# 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 <j...@jms.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