powerpc: Add virq_is_host to reduce virq_to_host usage

Some irq_host implementations are using virq_to_host to check if
they are the irq_host for a virtual irq.  To allow us to make space
versus time tradeoffs, replace this usage with an assertive
virq_is_host that confirms or denies the irq is associated with the
given irq_host.
Signed-off-by: Milton Miller <miltonm@bga.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/irq.h

@@ -128,6 +128,7 @@ struct irq_host {
 struct irq_data;
 extern irq_hw_number_t irqd_to_hwirq(struct irq_data *d);
 extern irq_hw_number_t virq_to_hw(unsigned int virq);
+extern bool virq_is_host(unsigned int virq, struct irq_host *host);
 extern struct irq_host *virq_to_host(unsigned int virq);
 
 /**

arch/powerpc/kernel/irq.c

@@ -510,6 +510,12 @@ irq_hw_number_t virq_to_hw(unsigned int virq)
 }
 EXPORT_SYMBOL_GPL(virq_to_hw);
 
+bool virq_is_host(unsigned int virq, struct irq_host *host)
+{
+	return irq_map[virq].host == host;
+}
+EXPORT_SYMBOL_GPL(virq_is_host);
+
 struct irq_host *virq_to_host(unsigned int virq)
 {
 	return irq_map[virq].host;

arch/powerpc/sysdev/xics/xics-common.c

@@ -213,7 +213,7 @@ void xics_migrate_irqs_away(void)
 		/* We can't set affinity on ISA interrupts */
 		if (virq < NUM_ISA_INTERRUPTS)
 			continue;
-		if (virq_to_host(virq) != xics_host)
+		if (!virq_is_host(virq, xics_host))
 			continue;
 		irq = (unsigned int)virq_to_hw(virq);
 		/* We need to get IPIs still. */