genirq: reenable a nobody cared disabled irq when a new driver arrives

Uwe Kleine-Koenig has some strange hardware where one of the shared
interrupts can be asserted during boot before the appropriate driver
loads. Requesting the shared irq line from another driver result in a
spurious interrupt storm which finally disables the interrupt line.

I have seen similar behaviour on resume before (the hardware does not
work anymore so I can not verify).

Change the spurious disable logic to increment the disable depth and
mark the interrupt with an extra flag which allows us to reenable the
interrupt when a new driver arrives which requests the same irq
line. In the worst case this will disable the irq again via the
spurious trap, but there is a decent chance that the new driver is the
one which can handle the already asserted interrupt and makes the box
usable again.

Eric Biederman said further: This case also happens on a regular basis
in kdump kernels where we deliberately don't shutdown the hardware
before starting the new kernel.  This patch should reduce the need for
using irqpoll in that situation by a small amount.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-and-Acked-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>

2 files changed, 34 insertions, 19 deletions

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 46e4ad1723f..46d6611a33b 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -150,6 +150,26 @@ void disable_irq(unsigned int irq)
 }
 EXPORT_SYMBOL(disable_irq);
 
+static void __enable_irq(struct irq_desc *desc, unsigned int irq)
+{
+	switch (desc->depth) {
+	case 0:
+		printk(KERN_WARNING "Unbalanced enable for IRQ %d\n", irq);
+		WARN_ON(1);
+		break;
+	case 1: {
+		unsigned int status = desc->status & ~IRQ_DISABLED;
+
+		/* Prevent probing on this irq: */
+		desc->status = status | IRQ_NOPROBE;
+		check_irq_resend(desc, irq);
+		/* fall-through */
+	}
+	default:
+		desc->depth--;
+	}
+}
+
 /**
  *	enable_irq - enable handling of an irq
  *	@irq: Interrupt to enable
@@ -169,22 +189,7 @@ void enable_irq(unsigned int irq)
 		return;
 
 	spin_lock_irqsave(&desc->lock, flags);
-	switch (desc->depth) {
-	case 0:
-		printk(KERN_WARNING "Unbalanced enable for IRQ %d\n", irq);
-		WARN_ON(1);
-		break;
-	case 1: {
-		unsigned int status = desc->status & ~IRQ_DISABLED;
-
-		/* Prevent probing on this irq: */
-		desc->status = status | IRQ_NOPROBE;
-		check_irq_resend(desc, irq);
-		/* fall-through */
-	}
-	default:
-		desc->depth--;
-	}
+	__enable_irq(desc, irq);
 	spin_unlock_irqrestore(&desc->lock, flags);
 }
 EXPORT_SYMBOL(enable_irq);
@@ -365,7 +370,7 @@ int setup_irq(unsigned int irq, struct irqaction *new)
 			compat_irq_chip_set_default_handler(desc);
 
 		desc->status &= ~(IRQ_AUTODETECT | IRQ_WAITING |
-				  IRQ_INPROGRESS);
+				  IRQ_INPROGRESS | IRQ_SPURIOUS_DISABLED);
 
 		if (!(desc->status & IRQ_NOAUTOEN)) {
 			desc->depth = 0;
@@ -381,6 +386,16 @@ int setup_irq(unsigned int irq, struct irqaction *new)
 	/* Reset broken irq detection when installing new handler */
 	desc->irq_count = 0;
 	desc->irqs_unhandled = 0;
+
+	/*
+	 * Check whether we disabled the irq via the spurious handler
+	 * before. Reenable it and give it another chance.
+	 */
+	if (shared && (desc->status & IRQ_SPURIOUS_DISABLED)) {
+		desc->status &= ~IRQ_SPURIOUS_DISABLED;
+		__enable_irq(desc, irq);
+	}
+
 	spin_unlock_irqrestore(&desc->lock, flags);
 
 	new->irq = irq;
diff --git a/kernel/irq/spurious.c b/kernel/irq/spurious.c
index 088dabbf2d6..c66d3f10e85 100644
--- a/kernel/irq/spurious.c
+++ b/kernel/irq/spurious.c
@@ -209,8 +209,8 @@ void note_interrupt(unsigned int irq, struct irq_desc *desc,
 		 * Now kill the IRQ
 		 */
 		printk(KERN_EMERG "Disabling IRQ #%d\n", irq);
-		desc->status |= IRQ_DISABLED;
-		desc->depth = 1;
+		desc->status |= IRQ_DISABLED | IRQ_SPURIOUS_DISABLED;
+		desc->depth++;
 		desc->chip->disable(irq);
 	}
 	desc->irqs_unhandled = 0;