GRETH: GBit transmit descriptor handling optimization
Daniel Hellstrom [Fri, 14 Jan 2011 03:02:39 +0000 (03:02 +0000)]
It is safe to enable all fragments before enabling the first descriptor,
this way all descriptors don't have to be processed twice, added extra
memory barrier.

Signed-off-by: Daniel Hellstrom <daniel@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/greth.c

index b307696..869e38d 100644 (file)
@@ -503,7 +503,7 @@ greth_start_xmit_gbit(struct sk_buff *skb, struct net_device *dev)
                greth->tx_skbuff[curr_tx] = NULL;
                bdp = greth->tx_bd_base + curr_tx;
 
-               status = GRETH_TXBD_CSALL;
+               status = GRETH_TXBD_CSALL | GRETH_BD_EN;
                status |= frag->size & GRETH_BD_LEN;
 
                /* Wrap around descriptor ring */
@@ -540,26 +540,27 @@ greth_start_xmit_gbit(struct sk_buff *skb, struct net_device *dev)
 
        wmb();
 
-       /* Enable the descriptors that we configured ...  */
-       for (i = 0; i < nr_frags + 1; i++) {
-               bdp = greth->tx_bd_base + greth->tx_next;
-               greth_write_bd(&bdp->stat, greth_read_bd(&bdp->stat) | GRETH_BD_EN);
-               greth->tx_next = NEXT_TX(greth->tx_next);
-               greth->tx_free--;
-       }
+       /* Enable the descriptor chain by enabling the first descriptor */
+       bdp = greth->tx_bd_base + greth->tx_next;
+       greth_write_bd(&bdp->stat, greth_read_bd(&bdp->stat) | GRETH_BD_EN);
+       greth->tx_next = curr_tx;
+       greth->tx_free -= nr_frags + 1;
+
+       wmb();
 
        greth_enable_tx(greth);
 
        return NETDEV_TX_OK;
 
 frag_map_error:
-       /* Unmap SKB mappings that succeeded */
+       /* Unmap SKB mappings that succeeded and disable descriptor */
        for (i = 0; greth->tx_next + i != curr_tx; i++) {
                bdp = greth->tx_bd_base + greth->tx_next + i;
                dma_unmap_single(greth->dev,
                                 greth_read_bd(&bdp->addr),
                                 greth_read_bd(&bdp->stat) & GRETH_BD_LEN,
                                 DMA_TO_DEVICE);
+               greth_write_bd(&bdp->stat, 0);
        }
 map_error:
        if (net_ratelimit())