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Commit 3b6330ce authored by Scott Wood's avatar Scott Wood Committed by Jeff Garzik
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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: default avatarScott Wood <scottwood@freescale.com>
Signed-off-by: default avatarJeff Garzik <jeff@garzik.org>
parent dbf2e858

drivers/net/gianfar.c

+11 −0
Original line number Diff line number Diff line
@@ -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 &