From 3b6330ce2a3e1f152f79a6203f73d23356e243a7 Mon Sep 17 00:00:00 2001 From: Scott Wood Date: Wed, 16 May 2007 15:06:59 -0500 Subject: [PATCH] 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 Signed-off-by: Jeff Garzik --- drivers/net/gianfar.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c index b666a0cc0642..f5b3cba23fc5 100644 --- a/drivers/net/gianfar.c +++ b/drivers/net/gianfar.c @@ -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 & -- 2.20.1