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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>
This commit is contained in:
Scott Wood 2007-05-16 15:06:59 -05:00 committed by Jeff Garzik
parent dbf2e85859
commit 3b6330ce2a
1 changed files with 11 additions and 0 deletions
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11
drivers/net/gianfar.c
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@ -1025,6 +1025,15 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
dev->trans_start = jiffies;
/* The powerpc-specific eieio() is used, as wmb() has too strong
* semantics (it requires synchronization between cacheable and
* uncacheable mappings, which eieio doesn't provide and which we
* don't need), thus requiring a more expensive sync instruction. At
* some point, the set of architecture-independent barrier functions
* should be expanded to include weaker barriers.
*/
eieio();
txbdp->status = status;
/* If this was the last BD in the ring, the next one */
@ -1301,6 +1310,7 @@ struct sk_buff * gfar_new_skb(struct net_device *dev, struct rxbd8 *bdp)
bdp->length = 0;
/* Mark the buffer empty */
eieio();
bdp->status |= (RXBD_EMPTY | RXBD_INTERRUPT);
return skb;
@ -1484,6 +1494,7 @@ int gfar_clean_rx_ring(struct net_device *dev, int rx_work_limit)
bdp = priv->cur_rx;
while (!((bdp->status & RXBD_EMPTY) || (--rx_work_limit < 0))) {
rmb();
skb = priv->rx_skbuff[priv->skb_currx];
if (!(bdp->status &