IRQ_NOPROBE helper functions

Probing non-ISA interrupts using the handle_percpu_irq as their handle_irq
method may crash the system because handle_percpu_irq does not check
IRQ_WAITING.  This for example hits the MIPS Qemu configuration.

This patch provides two helper functions set_irq_noprobe and set_irq_probe to
set rsp.  clear the IRQ_NOPROBE flag.  The only current caller is MIPS code
but this really belongs into generic code.

As an aside, interrupt probing these days has become a mostly obsolete if not
dangerous art.  I think Linux interrupts should be changed to default to
non-probing but that's subject of this patch.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Acked-and-tested-by: Rob Landley <rob@landley.net>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/irq.h

@@ -367,6 +367,9 @@ set_irq_chained_handler(unsigned int irq,
 	__set_irq_handler(irq, handle, 1, NULL);
 }
 
+extern void set_irq_noprobe(unsigned int irq);
+extern void set_irq_probe(unsigned int irq);
+
 /* Handle dynamic irq creation and destruction */
 extern int create_irq(void);
 extern void destroy_irq(unsigned int irq);

kernel/irq/chip.c

@@ -589,3 +589,39 @@ set_irq_chip_and_handler_name(unsigned int irq, struct irq_chip *chip,
 	set_irq_chip(irq, chip);
 	__set_irq_handler(irq, handle, 0, name);
 }
+
+void __init set_irq_noprobe(unsigned int irq)
+{
+	struct irq_desc *desc;
+	unsigned long flags;
+
+	if (irq >= NR_IRQS) {
+		printk(KERN_ERR "Trying to mark IRQ%d non-probeable\n", irq);
+
+		return;
+	}
+
+	desc = irq_desc + irq;
+
+	spin_lock_irqsave(&desc->lock, flags);
+	desc->status |= IRQ_NOPROBE;
+	spin_unlock_irqrestore(&desc->lock, flags);
+}
+
+void __init set_irq_probe(unsigned int irq)
+{
+	struct irq_desc *desc;
+	unsigned long flags;
+
+	if (irq >= NR_IRQS) {
+		printk(KERN_ERR "Trying to mark IRQ%d probeable\n", irq);
+
+		return;
+	}
+
+	desc = irq_desc + irq;
+
+	spin_lock_irqsave(&desc->lock, flags);
+	desc->status &= ~IRQ_NOPROBE;
+	spin_unlock_irqrestore(&desc->lock, flags);
+}