From: Lars Persson <lars.persson@axis.com>
Date: Fri, 1 Dec 2017 11:12:44 +0100
Subject: stmmac: reset last TSO segment size after device open
Git-commit: 45ab4b13e46325d00f4acdb365d406e941a15f81
Patch-mainline: v4.15-rc3
References: networking-stable-17_12_12

The mss variable tracks the last max segment size sent to the TSO
engine. We do not update the hardware as long as we receive skb:s with
the same value in gso_size.

During a network device down/up cycle (mapped to stmmac_release() and
stmmac_open() callbacks) we issue a reset to the hardware and it
forgets the setting for mss. However we did not zero out our mss
variable so the next transmission of a gso packet happens with an
undefined hardware setting.

This triggers a hang in the TSO engine and eventuelly the netdev
watchdog will bark.

Fixes: f748be531d70 ("stmmac: support new GMAC4")
Signed-off-by: Lars Persson <larper@axis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2566,6 +2566,7 @@ static int stmmac_open(struct net_device
 
 	priv->dma_buf_sz = STMMAC_ALIGN(buf_sz);
 	priv->rx_copybreak = STMMAC_RX_COPYBREAK;
+	priv->mss = 0;
 
 	ret = alloc_dma_desc_resources(priv);
 	if (ret < 0) {