Hi Bob,
On Wed, Apr 15, 2009 at 12:57 PM, Bob Copeland <me@xxxxxxxxxxxxxxx> wrote:
> This patch simplifies the code used to detect when the
> self-linked DMA buffer is still in use by hardware, by
> checking the hardware's rxdp register instead of looking
> at the software buffer list.
Just an observation: Each synchronous read over PCI will take at
minimum 0.9us to return. Accessing tables in the host's cache
hierarchy/memory will likely be much faster - possibly why it is done
like this already.
Is this a worthwhile tradeoff?
Many thanks,
Daniel
> Signed-off-by: Bob Copeland <me@xxxxxxxxxxxxxxx>
> ---
> drivers/net/wireless/ath/ath5k/base.c | 24 ++++--------------------
> drivers/net/wireless/ath/ath5k/base.h | 1 -
> drivers/net/wireless/ath/ath5k/dma.c | 2 --
> 3 files changed, 4 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath5k/base.c b/drivers/net/wireless/ath/ath5k/base.c
> index 3bde18f..1a6e72f 100644
> --- a/drivers/net/wireless/ath/ath5k/base.c
> +++ b/drivers/net/wireless/ath/ath5k/base.c
> @@ -1780,7 +1780,7 @@ ath5k_tasklet_rx(unsigned long data)
> struct sk_buff *skb, *next_skb;
> dma_addr_t next_skb_addr;
> struct ath5k_softc *sc = (void *)data;
> - struct ath5k_buf *bf, *bf_last;
> + struct ath5k_buf *bf;
> struct ath5k_desc *ds;
> int ret;
> int hdrlen;
> @@ -1791,7 +1791,6 @@ ath5k_tasklet_rx(unsigned long data)
> ATH5K_WARN(sc, "empty rx buf pool\n");
> goto unlock;
> }
> - bf_last = list_entry(sc->rxbuf.prev, struct ath5k_buf, list);
> do {
> rxs.flag = 0;
>
> @@ -1800,24 +1799,9 @@ ath5k_tasklet_rx(unsigned long data)
> skb = bf->skb;
> ds = bf->desc;
>
> - /*
> - * last buffer must not be freed to ensure proper hardware
> - * function. When the hardware finishes also a packet next to
> - * it, we are sure, it doesn't use it anymore and we can go on.
> - */
> - if (bf_last == bf)
> - bf->flags |= 1;
> - if (bf->flags) {
> - struct ath5k_buf *bf_next = list_entry(bf->list.next,
> - struct ath5k_buf, list);
> - ret = sc->ah->ah_proc_rx_desc(sc->ah, bf_next->desc,
> - &rs);
> - if (ret)
> - break;
> - bf->flags &= ~1;
> - /* skip the overwritten one (even status is martian) */
> - goto next;
> - }
> + /* bail if HW is still using self-linked descriptor */
> + if (ath5k_hw_get_rxdp(sc->ah) == bf->daddr)
> + break;
>
> ret = sc->ah->ah_proc_rx_desc(sc->ah, ds, &rs);
> if (unlikely(ret == -EINPROGRESS))
> diff --git a/drivers/net/wireless/ath/ath5k/base.h b/drivers/net/wireless/ath/ath5k/base.h
> index 8229561..852b2c1 100644
> --- a/drivers/net/wireless/ath/ath5k/base.h
> +++ b/drivers/net/wireless/ath/ath5k/base.h
> @@ -56,7 +56,6 @@
>
> struct ath5k_buf {
> struct list_head list;
> - unsigned int flags; /* rx descriptor flags */
> struct ath5k_desc *desc; /* virtual addr of desc */
> dma_addr_t daddr; /* physical addr of desc */
> struct sk_buff *skb; /* skbuff for buf */
> diff --git a/drivers/net/wireless/ath/ath5k/dma.c b/drivers/net/wireless/ath/ath5k/dma.c
> index b65b4fe..941b511 100644
> --- a/drivers/net/wireless/ath/ath5k/dma.c
> +++ b/drivers/net/wireless/ath/ath5k/dma.c
> @@ -80,8 +80,6 @@ int ath5k_hw_stop_rx_dma(struct ath5k_hw *ah)
> * ath5k_hw_get_rxdp - Get RX Descriptor's address
> *
> * @ah: The &struct ath5k_hw
> - *
> - * XXX: Is RXDP read and clear ?
> */
> u32 ath5k_hw_get_rxdp(struct ath5k_hw *ah)
> {
--
Daniel J Blueman
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