net/macb: memory barriers cleanup

Remove a couple of unneeded barriers and document the remaining ones.

Signed-off-by: Havard Skinnemoen <havard@skinnemoen.net>
[nicolas.ferre@atmel.com: split patch in topics]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/cadence/macb.c b/drivers/net/ethernet/cadence/macb.c
index 0931cb7..e7f554d 100644 (file)
--- a/drivers/net/ethernet/cadence/macb.c
+++ b/drivers/net/ethernet/cadence/macb.c
@@ -373,7 +373,9 @@ static void macb_tx(struct macb *bp)
 
                BUG_ON(skb == NULL);
 
+               /* Make hw descriptor updates visible to CPU */
                rmb();
+
                bufstat = bp->tx_ring[tail].ctrl;
 
                if (!(bufstat & MACB_BIT(TX_USED)))
@@ -416,7 +418,10 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
                        if (frag == last_frag)
                                break;
                }
+
+               /* Make descriptor updates visible to hardware */
                wmb();
+
                return 1;
        }
 
@@ -437,12 +442,14 @@ static int macb_rx_frame(struct macb *bp, unsigned int first_frag,
                                               frag_len);
                offset += RX_BUFFER_SIZE;
                bp->rx_ring[frag].addr &= ~MACB_BIT(RX_USED);
-               wmb();
 
                if (frag == last_frag)
                        break;
        }
 
+       /* Make descriptor updates visible to hardware */
+       wmb();
+
        skb->protocol = eth_type_trans(skb, bp->dev);
 
        bp->stats.rx_packets++;
@@ -462,6 +469,8 @@ static void discard_partial_frame(struct macb *bp, unsigned int begin,
 
        for (frag = begin; frag != end; frag = NEXT_RX(frag))
                bp->rx_ring[frag].addr &= ~MACB_BIT(RX_USED);
+
+       /* Make descriptor updates visible to hardware */
        wmb();
 
        /*
@@ -480,7 +489,9 @@ static int macb_rx(struct macb *bp, int budget)
        for (; budget > 0; tail = NEXT_RX(tail)) {
                u32 addr, ctrl;
 
+               /* Make hw descriptor updates visible to CPU */
                rmb();
+
                addr = bp->rx_ring[tail].addr;
                ctrl = bp->rx_ring[tail].ctrl;
 
@@ -675,6 +686,8 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
        bp->tx_ring[entry].addr = mapping;
        bp->tx_ring[entry].ctrl = ctrl;
+
+       /* Make newly initialized descriptor visible to hardware */
        wmb();
 
        entry = NEXT_TX(entry);
@@ -783,9 +796,6 @@ static void macb_init_rings(struct macb *bp)
 
 static void macb_reset_hw(struct macb *bp)
 {
-       /* Make sure we have the write buffer for ourselves */
-       wmb();
-
        /*
         * Disable RX and TX (XXX: Should we halt the transmission
         * more gracefully?)