sungem: Soft lockup in sungem on Netra AC200 when switching interface up

From: Ilkka Virta <itvirta@iki.fi>

In the lockup situation the driver seems to go off in an eternal storm
of interrupts right after calling request_irq(). It doesn't actually
do anything interesting in the interrupt handler. Since connecting the link
afterwards works, something later in initialization must fix this.

Looking at gem_do_start() and gem_open(), it seems that the only thing
done while opening the device after the request_irq(), is a call to
napi_enable().

I don't know what the ordering requirements are for the
initialization, but I boldly tried to move the napi_enable() call
inside gem_do_start() before the link state is checked and interrupts
subsequently enabled, and it seems to work for me. Doesn't even break
anything too obvious...
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/sungem.c

@@ -2221,6 +2221,8 @@ static int gem_do_start(struct net_device *dev)
 
 	gp->running = 1;
 
+	napi_enable(&gp->napi);
+
 	if (gp->lstate == link_up) {
 		netif_carrier_on(gp->dev);
 		gem_set_link_modes(gp);
@@ -2238,6 +2240,8 @@ static int gem_do_start(struct net_device *dev)
 		spin_lock_irqsave(&gp->lock, flags);
 		spin_lock(&gp->tx_lock);
 
+		napi_disable(&gp->napi);
+
 		gp->running =  0;
 		gem_reset(gp);
 		gem_clean_rings(gp);
@@ -2338,8 +2342,6 @@ static int gem_open(struct net_device *dev)
 	if (!gp->asleep)
 		rc = gem_do_start(dev);
 	gp->opened = (rc == 0);
-	if (gp->opened)
-		napi_enable(&gp->napi);
 
 	mutex_unlock(&gp->pm_mutex);
 
@@ -2476,8 +2478,6 @@ static int gem_resume(struct pci_dev *pdev)
 
 		/* Re-attach net device */
 		netif_device_attach(dev);
-
-		napi_enable(&gp->napi);
 	}
 
 	spin_lock_irqsave(&gp->lock, flags);