gianfar: Add I/O barriers when touching buffer descriptor ownership.
The hardware must not see that is given ownership of a buffer until it is completely written, and when the driver receives ownership of a buffer, it must ensure that any other reads to the buffer reflect its final state. Thus, I/O barriers are added where required. Without this patch, I have observed GCC reordering the setting of bdp->length and bdp->status in gfar_new_skb. Hardware reordering was also theoretically possible. Signed-off-by: Scott Wood <scottwood@freescale.com> Signed-off-by: Jeff Garzik <jeff@garzik.org>
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@ -1025,6 +1025,15 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
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dev->trans_start = jiffies;
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/* The powerpc-specific eieio() is used, as wmb() has too strong
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* semantics (it requires synchronization between cacheable and
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* uncacheable mappings, which eieio doesn't provide and which we
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* don't need), thus requiring a more expensive sync instruction. At
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* some point, the set of architecture-independent barrier functions
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* should be expanded to include weaker barriers.
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*/
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eieio();
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txbdp->status = status;
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/* If this was the last BD in the ring, the next one */
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@ -1301,6 +1310,7 @@ struct sk_buff * gfar_new_skb(struct net_device *dev, struct rxbd8 *bdp)
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bdp->length = 0;
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/* Mark the buffer empty */
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eieio();
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bdp->status |= (RXBD_EMPTY | RXBD_INTERRUPT);
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return skb;
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@ -1484,6 +1494,7 @@ int gfar_clean_rx_ring(struct net_device *dev, int rx_work_limit)
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bdp = priv->cur_rx;
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while (!((bdp->status & RXBD_EMPTY) || (--rx_work_limit < 0))) {
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rmb();
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skb = priv->rx_skbuff[priv->skb_currx];
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if (!(bdp->status &
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