Bug#415476: natsemi: Fix for interrupt sharing issue

[Mark Brown <broonie@debian.org>]

Package: linux-image-2.6.18-4
Severity: important
Tags: patch

Kernel 2.6.18 contains a version of the natsemi driver which supports
NAPI but has buggy handling of shared interrupts.  The patch below
(which is a slightly cut down version of one which has been accepted
upstream, omitting reversion of another change which worked around this
problem) fixes this.  The active part of the patch is the very first
chnage.

Severity important since this can cause the driver to hang on machines
where a natsemi device shares an interrupt.

Subject: natsemi: Fix NAPI for interrupt sharing

The interrupt status register for the natsemi chips is clear on read and
was read unconditionally from both the interrupt and from the NAPI poll
routine, meaning that if the interrupt service routine was called (for 
example, due to a shared interrupt) while a NAPI poll was scheduled
interrupts could be missed.  This patch fixes that by ensuring that the
interrupt status register is only read by the interrupt handler when
interrupts are enabled from the chip.

Thanks to Sergei Shtylyov <sshtylyov@ru.mvista.com> for spotting the
issue, Mark Huth <mhuth@mvista.com> for a simpler method and Simon
Blake <simon@citylink.co.nz> for testing resources.

Index: linux-2.6/drivers/net/natsemi.c
===================================================================
--- linux-2.6.orig/drivers/net/natsemi.c	2007-03-11 02:32:43.000000000 +0000
+++ linux-2.6/drivers/net/natsemi.c	2007-03-13 19:38:31.000000000 +0000
@@ -2119,28 +2119,35 @@
 	struct netdev_private *np = netdev_priv(dev);
 	void __iomem * ioaddr = ns_ioaddr(dev);
 
-	if (np->hands_off)
+	/* Reading IntrStatus automatically acknowledges so don't do
+	 * that while interrupts are disabled, (for example, while a
+	 * poll is scheduled).  */
+	if (np->hands_off || !readl(ioaddr + IntrEnable))
 		return IRQ_NONE;
 
-	/* Reading automatically acknowledges. */
 	np->intr_status = readl(ioaddr + IntrStatus);
 
+	if (!np->intr_status)
+		return IRQ_NONE;
+
 	if (netif_msg_intr(np))
 		printk(KERN_DEBUG
 		       "%s: Interrupt, status %#08x, mask %#08x.\n",
 		       dev->name, np->intr_status,
 		       readl(ioaddr + IntrMask));
 
-	if (!np->intr_status)
-		return IRQ_NONE;
-
 	prefetch(&np->rx_skbuff[np->cur_rx % RX_RING_SIZE]);
 
 	if (netif_rx_schedule_prep(dev)) {
 		/* Disable interrupts and register for poll */
 		natsemi_irq_disable(dev);
 		__netif_rx_schedule(dev);
-	}
+	} else
+		printk(KERN_WARNING
+	       	       "%s: Ignoring interrupt, status %#08x, mask %#08x.\n",
+		       dev->name, np->intr_status,
+		       readl(ioaddr + IntrMask));
+
 	return IRQ_HANDLED;
 }
 
@@ -2156,6 +2163,12 @@
 	int work_done = 0;
 
 	do {
+		if (netif_msg_intr(np))
+			printk(KERN_DEBUG
+			       "%s: Poll, status %#08x, mask %#08x.\n",
+			       dev->name, np->intr_status,
+			       readl(ioaddr + IntrMask));
+
 		if (np->intr_status &
 		    (IntrTxDone | IntrTxIntr | IntrTxIdle | IntrTxErr)) {
 			spin_lock(&np->lock);

-- System Information:
Debian Release: 4.0
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: powerpc (ppc)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.6.18-3-powerpc
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)