[PATCH 092/222] net:fec: quiesce packet processing before changing features

[Russell King]

Changing the features (receive checksumming) requires the hardware to be
reprogrammed, and also changes the checks in the receive packet
processing.

The current implementation has a race - fec_set_features() changes the
flags which alter the receive packet processing while we are active.
Only afterwards do we shutdown and reconfigure the hardware.

This can lead to packets being received and marked with a valid checksum
(via CHECKSUM_UNNECESSARY) when the hardware checksum validation has not
yet been enabled.

We must quiesce the device, then change the software configuration for
this feature, and then resume the device if it was previously running.

The resulting code structure also allows us to add other configuration
features in this path without having to quiesce and resume the network
interface and device.

Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 drivers/net/ethernet/freescale/fec_main.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 789678c6f6d4..c5a5a0aedf21 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -1993,12 +1993,21 @@ static void fec_poll_controller(struct net_device *dev)
 }
 #endif
 
+#define FEATURES_NEED_QUIESCE NETIF_F_RXCSUM
+
 static int fec_set_features(struct net_device *netdev,
 	netdev_features_t features)
 {
 	struct fec_enet_private *fep = netdev_priv(netdev);
 	netdev_features_t changed = features ^ netdev->features;
 
+	/* Quiesce the device if necessary */
+	if (netif_running(netdev) && changed & FEATURES_NEED_QUIESCE) {
+		napi_disable(&fep->napi);
+		netif_tx_lock_bh(netdev);
+		fec_stop(netdev);
+	}
+
 	netdev->features = features;
 
 	/* Receive checksum has been changed */
@@ -2007,16 +2016,14 @@ static int fec_set_features(struct net_device *netdev,
 			fep->csum_flags |= FLAG_RX_CSUM_ENABLED;
 		else
 			fep->csum_flags &= ~FLAG_RX_CSUM_ENABLED;
+	}
 
-		if (netif_running(netdev)) {
-			napi_disable(&fep->napi);
-			netif_tx_lock_bh(netdev);
-			fec_stop(netdev);
-			fec_restart(netdev, fep->phy_dev->duplex);
-			netif_wake_queue(netdev);
-			netif_tx_unlock_bh(netdev);
-			napi_enable(&fep->napi);
-		}
+	/* Resume the device after updates */
+	if (netif_running(netdev) && changed & FEATURES_NEED_QUIESCE) {
+		fec_restart(netdev, fep->phy_dev->duplex);
+		netif_wake_queue(netdev);
+		netif_tx_unlock_bh(netdev);
+		napi_enable(&fep->napi);
 	}
 
 	return 0;
-- 
1.8.3.1