gianfar: Change default HW Tx queue scheduling mode

commit b98b8babd6e3370fadb7c6eaacb00eb2f6344a6c upstream.

This is primarily to address transmission timeout occurrences, when
multiple H/W Tx queues are being used concurrently. Because in
the priority scheduling mode the controller does not service the
Tx queues equally (but in ascending index order), Tx timeouts are
being triggered rightaway for a basic test with multiple simultaneous
connections like:
iperf -c <server_ip> -n 100M -P 8

resulting in kernel trace:
NETDEV WATCHDOG: eth1 (fsl-gianfar): transmit queue <X> timed out
------------[ cut here ]------------
WARNING: at net/sched/sch_generic.c:255
...
and controller reset during intense traffic, and possibly further
complications.

This patch changes the default H/W Tx scheduling setting (TXSCHED)
for multi-queue devices, from priority scheduling mode to a weighted
round robin mode with equal weights for all H/W Tx queues, and
addresses the issue above.

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index d0722a7d480b..fb9e7d34bcf2 100644
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c
@@ -397,7 +397,13 @@ static void gfar_init_mac(struct net_device *ndev)
 	if (ndev->features & NETIF_F_IP_CSUM)
 		tctrl |= TCTRL_INIT_CSUM;
 
-	tctrl |= TCTRL_TXSCHED_PRIO;
+	if (priv->prio_sched_en)
+		tctrl |= TCTRL_TXSCHED_PRIO;
+	else {
+		tctrl |= TCTRL_TXSCHED_WRRS;
+		gfar_write(&regs->tr03wt, DEFAULT_WRRS_WEIGHT);
+		gfar_write(&regs->tr47wt, DEFAULT_WRRS_WEIGHT);
+	}
 
 	gfar_write(&regs->tctrl, tctrl);
 
@@ -1157,6 +1163,9 @@ static int gfar_probe(struct platform_device *ofdev)
 	priv->rx_filer_enable = 1;
 	/* Enable most messages by default */
 	priv->msg_enable = (NETIF_MSG_IFUP << 1 ) - 1;
+	/* use pritority h/w tx queue scheduling for single queue devices */
+	if (priv->num_tx_queues == 1)
+		priv->prio_sched_en = 1;
 
 	/* Carrier starts down, phylib will bring it up */
 	netif_carrier_off(dev);