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>
diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index b666a0c..f5b3cba 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -1025,6 +1025,15 @@
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 @@
bdp->length = 0;
/* Mark the buffer empty */
+ eieio();
bdp->status |= (RXBD_EMPTY | RXBD_INTERRUPT);
return skb;
@@ -1484,6 +1494,7 @@
bdp = priv->cur_rx;
while (!((bdp->status & RXBD_EMPTY) || (--rx_work_limit < 0))) {
+ rmb();
skb = priv->rx_skbuff[priv->skb_currx];
if (!(bdp->status &