gianfar: Add I/O barriers when touching buffer descriptor ownership. (3b6330ce) · Commits · 戴 / test

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>

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 &

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