8139too: move wmb before TX DMA start

The write barrier should be used before starting a DMA transfer. This fixes
a problem, where almost all packets received on another machine had garbled
content. Tested with an RTL8100C on a MIPS machine.

Signed-off-by: Andreas Oberritter <obi@linuxtv.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/net/8139too.c b/drivers/net/8139too.c
index 32e66f0d4344..0daf8c15e381 100644
--- a/drivers/net/8139too.c
+++ b/drivers/net/8139too.c
@@ -1723,13 +1723,18 @@ static int rtl8139_start_xmit (struct sk_buff *skb, struct net_device *dev)
         }
 
         spin_lock_irqsave(&tp->lock, flags);
+        /*
+         * Writing to TxStatus triggers a DMA transfer of the data
+         * copied to tp->tx_buf[entry] above. Use a memory barrier
+         * to make sure that the device sees the updated data.
+         */
+        wmb();
         RTL_W32_F (TxStatus0 + (entry * sizeof (u32)),
                    tp->tx_flag | max(len, (unsigned int)ETH_ZLEN));
 
         dev->trans_start = jiffies;
 
         tp->cur_tx++;
-        wmb();
 
         if ((tp->cur_tx - NUM_TX_DESC) == tp->dirty_tx)
                 netif_stop_queue (dev);