irq: Fix check for already initialized irq_domain in irq_domain_add

The sanity check in irq_domain_add() tests desc->irq_data != NULL or
irq_data->domain != NULL. This prevents adding an irq_domain to a irq
descriptor when irq_data exists, which true when the irq descriptor
exists.

This went unnoticed so far as the simple domain code did not enter
this code path because domain->nr_irqs is always 0 for the simple domains.

Split the check for irq_data == NULL out and have a separate warning
for it.

[ tglx: Made the check for irq_data == NULL separate ]

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: marc.zyngier@arm.com
Cc: thomas.abraham@linaro.org
Cc: jamie@jamieiles.com
Cc: b-cousson@ti.com
Cc: shawn.guo@linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: devicetree-discuss@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1316017900-19918-3-git-send-email-robherring2@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/irqdomain.c

@@ -29,7 +29,11 @@ void irq_domain_add(struct irq_domain *domain)
 	 */
 	for (hwirq = 0; hwirq < domain->nr_irq; hwirq++) {
 		d = irq_get_irq_data(irq_domain_to_irq(domain, hwirq));
-		if (d || d->domain) {
+		if (!d) {
+			WARN(1, "error: assigning domain to non existant irq_desc");
+			return;
+		}
+		if (d->domain) {
 			/* things are broken; just report, don't clean up */
 			WARN(1, "error: irq_desc already assigned to a domain");
 			return;