stmmac: reset last TSO segment size after device open

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.

---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 1 +
 1 file changed, 1 insertion(+)

index f63c2ddced3c..d7250539d0bd 100644
@@ -2588,6 +2588,7 @@ static int stmmac_open(struct net_device *dev)
 
 	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) {

2.11.0

From: Lars Persson <[email protected]>
Date: Fri, 1 Dec 2017 11:12:44 +0100

Applied and queued up for -stable, thanks.