net: smsc911x: Quieten netif during suspend

If the network interface is kept running during suspend, the net core
may call net_device_ops.ndo_start_xmit() while the Ethernet device is
still suspended, which may lead to a system crash.

E.g. on sh73a0/kzm9g and r8a73a4/ape6evm, the external Ethernet chip is
driven by a PM controlled clock.  If the Ethernet registers are accessed
while the clock is not running, the system will crash with an imprecise
external abort.

As this is a race condition with a small time window, it is not so easy
to trigger at will.  Using pm_test may increase your chances:

    # echo 0 > /sys/module/printk/parameters/console_suspend
    # echo platform > /sys/power/pm_test
    # echo mem > /sys/power/state

To fix this, make sure the network interface is quietened during
suspend.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/smsc/smsc911x.c

@@ -2595,6 +2595,11 @@ static int smsc911x_suspend(struct device *dev)
 	struct net_device *ndev = dev_get_drvdata(dev);
 	struct smsc911x_data *pdata = netdev_priv(ndev);
 
+	if (netif_running(ndev)) {
+		netif_stop_queue(ndev);
+		netif_device_detach(ndev);
+	}
+
 	/* enable wake on LAN, energy detection and the external PME
 	 * signal. */
 	smsc911x_reg_write(pdata, PMT_CTRL,
@@ -2628,7 +2633,15 @@ static int smsc911x_resume(struct device *dev)
 	while (!(smsc911x_reg_read(pdata, PMT_CTRL) & PMT_CTRL_READY_) && --to)
 		udelay(1000);
 
-	return (to == 0) ? -EIO : 0;
+	if (to == 0)
+		return -EIO;
+
+	if (netif_running(ndev)) {
+		netif_device_attach(ndev);
+		netif_start_queue(ndev);
+	}
+
+	return 0;
 }
 
 static const struct dev_pm_ops smsc911x_pm_ops = {