this is an example of how a simple 8313 Periodic Interval Timer (PIT) kernel driver
registers for the PIT IRQ (Interrupt ID 65)

#define PIT_IRQ 65

    virq = irq_create_mapping(NULL, PIT_IRQ);
    set_irq_type(virq, IRQ_TYPE_LEVEL_LOW);

    if(request_irq(virq, (irq_handler_t)timerEvent, 0, "timer2", (void *)0)) {
        printk(KERN_ERR "request_irq() returned error for irq=%d virq=%d\n", PIT_IRQ, virq);
    }

It is some time ago, but when I did something similar I needed the
following patch in order to use NULL for irq_create_mapping(). Have a
try, and if it is still needed (as it looks from a glimpse), then maybe
we should get it merged?

===

From: Wolfram Sang <redacted>
Subject: [PATCH] powerpc/cpm2: make cpm2_pic the default host

Signed-off-by: Wolfram Sang <redacted>
---
 arch/powerpc/sysdev/cpm2_pic.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/sysdev/cpm2_pic.c b/arch/powerpc/sysdev/cpm2_pic.c
index 78f1f7c..7a7d4e5 100644
--- a/arch/powerpc/sysdev/cpm2_pic.c
+++ b/arch/powerpc/sysdev/cpm2_pic.c

@@ -272,4 +272,5 @@ void cpm2_pic_init(struct device_node *node)
 		printk(KERN_ERR "CPM2 PIC: failed to allocate irq host!\n");
 		return;
 	}
+	irq_set_default_host(cpm2_pic_host);
 }

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |