[POWERPC] Add irq_create_direct_mapping()

This patch adds irq_create_direct_mapping().  This routine is
an alternative to irq_create_mapping(), for irq controllers that
can use linux virq numbers directly as hardware numbers.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/irq.c

@@ -616,6 +616,30 @@ static int irq_setup_virq(struct irq_host *host, unsigned int virq,
 	return 0;
 }
 
+unsigned int irq_create_direct_mapping(struct irq_host *host)
+{
+	unsigned int virq;
+
+	if (host == NULL)
+		host = irq_default_host;
+
+	BUG_ON(host == NULL);
+	WARN_ON(host->revmap_type != IRQ_HOST_MAP_NOMAP);
+
+	virq = irq_alloc_virt(host, 1, 0);
+	if (virq == NO_IRQ) {
+		pr_debug("irq: create_direct virq allocation failed\n");
+		return NO_IRQ;
+	}
+
+	pr_debug("irq: create_direct obtained virq %d\n", virq);
+
+	if (irq_setup_virq(host, virq, virq))
+		return NO_IRQ;
+
+	return virq;
+}
+
 unsigned int irq_create_mapping(struct irq_host *host,
 				irq_hw_number_t hwirq)
 {

include/asm-powerpc/irq.h

@@ -223,6 +223,15 @@ extern void irq_dispose_mapping(unsigned int virq);
 extern unsigned int irq_find_mapping(struct irq_host *host,
 				     irq_hw_number_t hwirq);
 
+/**
+ * irq_create_direct_mapping - Allocate a virq for direct mapping
+ * @host: host to allocate the virq for or NULL for default host
+ *
+ * This routine is used for irq controllers which can choose the hardware
+ * interrupt numbers they generate. In such a case it's simplest to use
+ * the linux virq as the hardware interrupt number.
+ */
+extern unsigned int irq_create_direct_mapping(struct irq_host *host);
 
 /**
  * irq_radix_revmap - Find a linux virq from a hw irq number.