On Mon, 2013-08-26 at 17:45 -0500, Rob Herring wrote:
> From: Rob Herring <rob.herr...@calxeda.com>
>
> Since the xgmac transmit start and completion work locklessly, it is
> possible for xgmac_xmit to stop the tx queue after the xgmac_tx_complete
> has run resulting in the tx queue never being woken up. Fix this by
> ensuring that ring buffer index updates are visible and serialize the
> queue wake with netif_tx_lock.
>
> The implementation used here was copied from
> drivers/net/ethernet/broadcom/tg3.c.
>
> Signed-off-by: Rob Herring <rob.herr...@calxeda.com>
> ---
> drivers/net/ethernet/calxeda/xgmac.c | 25 +++++++++++++++++++------
> 1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/calxeda/xgmac.c
> b/drivers/net/ethernet/calxeda/xgmac.c
> index f630855..cd5872c 100644
> --- a/drivers/net/ethernet/calxeda/xgmac.c
> +++ b/drivers/net/ethernet/calxeda/xgmac.c
> @@ -410,6 +410,9 @@ struct xgmac_priv {
> #define dma_ring_space(h, t, s) CIRC_SPACE(h, t, s)
> #define dma_ring_cnt(h, t, s) CIRC_CNT(h, t, s)
>
> +#define tx_dma_ring_space(p) \
> + dma_ring_space((p)->tx_head, (p)->tx_tail, DMA_TX_RING_SZ)
> +
> /* XGMAC Descriptor Access Helpers */
> static inline void desc_set_buf_len(struct xgmac_dma_desc *p, u32 buf_sz)
> {
> @@ -886,9 +889,14 @@ static void xgmac_tx_complete(struct xgmac_priv *priv)
> priv->tx_tail = dma_ring_incr(entry, DMA_TX_RING_SZ);
> }
>
> - if (dma_ring_space(priv->tx_head, priv->tx_tail, DMA_TX_RING_SZ) >
> - MAX_SKB_FRAGS)
> - netif_wake_queue(priv->dev);
> + /* Ensure tx_tail is visible to xgmac_xmit */
> + smp_mb();
> + if (unlikely(netif_queue_stopped(priv->dev))) {
> + netif_tx_lock(priv->dev);
> + if (tx_dma_ring_space(priv) > MAX_SKB_FRAGS)
> + netif_wake_queue(priv->dev);
> + netif_tx_unlock(priv->dev);
> + }
> }
You don't need to take the TX lock for this. The memory barriers
provide sufficient synchronisation.
> static void xgmac_tx_timeout_work(struct work_struct *work)
> @@ -1125,10 +1133,15 @@ static netdev_tx_t xgmac_xmit(struct sk_buff *skb,
> struct net_device *dev)
>
> priv->tx_head = dma_ring_incr(entry, DMA_TX_RING_SZ);
>
> - if (dma_ring_space(priv->tx_head, priv->tx_tail, DMA_TX_RING_SZ) <
> - MAX_SKB_FRAGS)
> + /* Ensure tx_head update is visible to tx completion */
> + smp_mb();
> + if (unlikely(tx_dma_ring_space(priv) < MAX_SKB_FRAGS)) {
> netif_stop_queue(dev);
> -
> + /* Ensure netif_stop_queue is visible to tx completion */
> + smp_mb();
> + if (tx_dma_ring_space(priv) > MAX_SKB_FRAGS)
> + netif_wake_queue(dev);
You should use netif_start_queue() rather than netif_wake_queue(), since
you know the TX scheduler is already active.
Ben.
> + }
> return NETDEV_TX_OK;
> }
>
--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
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