target/linux/leon/patches/020-greth_optimize_gbit_tx_descriptor_handling.patch

   1 From 544631281bed5cc37b8f2d3a99f44c9d4b97f9a8 Mon Sep 17 00:00:00 2001
   2 From: Daniel Hellstrom <daniel@gaisler.com>
   3 Date: Wed, 1 Dec 2010 10:07:12 +0100
   4 Subject: [PATCH] GRETH: GBit transmit descriptor handling optimization
   5
   6 It is safe to enable all fragments before enabling the first descriptor,
   7 this way all descriptors don't have to be processed twice, added extra
   8 memory barrier.
   9
  10 Signed-off-by: Daniel Hellstrom <daniel@gaisler.com>
  11 ---
  12  drivers/net/greth.c |   19 ++++++++++---------
  13  1 files changed, 10 insertions(+), 9 deletions(-)
  14
  15 --- a/drivers/net/greth.c
  16 +++ b/drivers/net/greth.c
  17 @@ -512,7 +512,7 @@ greth_start_xmit_gbit(struct sk_buff *sk
  18                 greth->tx_skbuff[curr_tx] = NULL;
  19                 bdp = greth->tx_bd_base + curr_tx;
  20
  21 -               status = GRETH_TXBD_CSALL;
  22 +               status = GRETH_TXBD_CSALL | GRETH_BD_EN;
  23                 status |= frag->size & GRETH_BD_LEN;
  24
  25                 /* Wrap around descriptor ring */
  26 @@ -549,26 +549,27 @@ greth_start_xmit_gbit(struct sk_buff *sk
  27
  28         wmb();
  29
  30 -       /* Enable the descriptors that we configured ...  */
  31 -       for (i = 0; i < nr_frags + 1; i++) {
  32 -               bdp = greth->tx_bd_base + greth->tx_next;
  33 -               greth_write_bd(&bdp->stat, greth_read_bd(&bdp->stat) | GRETH_BD_EN);
  34 -               greth->tx_next = NEXT_TX(greth->tx_next);
  35 -               greth->tx_free--;
  36 -       }
  37 +       /* Enable the descriptor chain by enabling the first descriptor */
  38 +       bdp = greth->tx_bd_base + greth->tx_next;
  39 +       greth_write_bd(&bdp->stat, greth_read_bd(&bdp->stat) | GRETH_BD_EN);
  40 +       greth->tx_next = curr_tx;
  41 +       greth->tx_free -= nr_frags + 1;
  42 +
  43 +       wmb();
  44
  45         greth_enable_tx(greth);
  46
  47         return NETDEV_TX_OK;
  48
  49  frag_map_error:
  50 -       /* Unmap SKB mappings that succeeded */
  51 +       /* Unmap SKB mappings that succeeded and disable descriptor */
  52         for (i = 0; greth->tx_next + i != curr_tx; i++) {
  53                 bdp = greth->tx_bd_base + greth->tx_next + i;
  54                 dma_unmap_single(greth->dev,
  55                                  greth_read_bd(&bdp->addr),
  56                                  greth_read_bd(&bdp->stat) & GRETH_BD_LEN,
  57                                  DMA_TO_DEVICE);
  58 +               greth_write_bd(&bdp->stat, 0);
  59         }
  60  map_error:
  61         if (net_ratelimit())