From 5b3b32d061477e99d0805197930ad60dd51909d6 Mon Sep 17 00:00:00 2001 From: Niklas Cassel Date: Mon, 26 Feb 2018 22:47:06 +0100 Subject: net: stmmac: ensure that the MSS desc is the last desc to set the own bit [ Upstream commit 15d2ee42a3087089e73ad52fd8c1b37ab496b87c ] A dma_wmb() is used to guarantee the ordering, with respect to other writes, to cache coherent DMA memory. There is a dma_wmb() in prepare_tx_desc()/prepare_tso_tx_desc() which ensures that TDES0/1/2 is written before TDES3 (which contains the own bit), for First Desc. However, in the rare case that MSS changes, there will be a MSS context descriptor in front of the regular DMA descriptors: <- DMA Next Descriptor Thus, for this special case, we need a dma_wmb() after prepare_tso_tx_desc()/before writing the own bit to the MSS desc, so that we flush the write to TDES3 for First Desc, in order to ensure that the MSS descriptor is the last descriptor to set the own bit. Signed-off-by: Niklas Cassel Signed-off-by: David S. Miller Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'drivers') diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index 34692fea8fbf..b3bc1287b2a7 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -2141,8 +2141,15 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev) tcp_hdrlen(skb) / 4, (skb->len - proto_hdr_len)); /* If context desc is used to change MSS */ - if (mss_desc) + if (mss_desc) { + /* Make sure that first descriptor has been completely + * written, including its own bit. This is because MSS is + * actually before first descriptor, so we need to make + * sure that MSS's own bit is the last thing written. + */ + dma_wmb(); priv->hw->desc->set_tx_owner(mss_desc); + } /* The own bit must be the latest setting done when prepare the * descriptor and then barrier is needed to make sure that -- cgit v1.2.3