netdev: bfin_mac: fix malformed UDP packet transmission when polling with KGDB

Writes to the DMA descriptors may sit in the internal Blackfin data buffers
and not actually be available when the DMA engine goes to fetch them.  This
does not typically happen, but when dealing with short/fast packets such as
UDP and polling KGDB, this occurs much more frequently.  Same goes for
heavy loads as seen by netperf tests or large scp transfers.  So force the
buffers to drain with SSYNC otherwise we get random malformed packets.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/bfin_mac.c b/drivers/net/bfin_mac.c
index 1905532d0940db6e38f7de2a90b0996a38d372e8..38d34cec65a36f40e8ef57a21470ac654f433540 100644 (file)
--- a/drivers/net/bfin_mac.c
+++ b/drivers/net/bfin_mac.c
@@ -688,6 +688,12 @@ static int bfin_mac_hard_start_xmit(struct sk_buff *skb,
                }
        }
 
+       /* make sure the internal data buffers in the core are drained
+        * so that the DMA descriptors are completely written when the
+        * DMA engine goes to fetch them below
+        */
+       SSYNC();
+
        /* enable this packet's dma */
        current_tx_ptr->desc_a.config |= DMAEN;