[PATCH 096/222] net:fec: add barrier to transmit path to ensure proper ordering

[Russell King]

Ensure that the writes to the descriptor data is visible to the hardware
before the descriptor is handed over to the hardware.

Having discussed this with Will Deacon, we need a wmb() between writing
the descriptor data and handing the descriptor over to the hardware.
The corresponding rmb() is in the ethernet hardware.

Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 drivers/net/ethernet/freescale/fec_main.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index d5ad0c70e6a0..2d9a6493b33b 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -436,6 +436,13 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 		}
 	}
 
+	/*
+	 * We need the preceding stores to the descriptor to complete
+	 * before updating the status field, which hands it over to the
+	 * hardware.  The corresponding rmb() is "in the hardware".
+	 */
+	wmb();
+
 	/* Send it on its way.  Tell FEC it's ready, interrupt when done,
 	 * it's the last BD of the frame, and to put the CRC on the end.
 	 */
-- 
1.8.3.1