of: irq: use of_irq_get() in of_irq_to_resource()

of_irq_to_resource() currently uses irq_of_parse_and_map() to
translate a DT interrupt specification into a Linux virtual interrupt
number. While this works in most cases, irq_of_parse_and_map() doesn't
properly handle the case where the interrupt controller is not yet
available (due to deferred probing for example).

So instead, use of_irq_get(), which is implemented exactly like
irq_of_parse_and_map(), with the exception that if the interrupt
controller is not yet available, it returns -EPROBE_DEFER. Obviously,
we also handle this error and bail out from of_irq_to_resource() when
of_irq_get() returns an error.

This allows to avoid silly error messages at boot time caused by
irq_create_of_mapping() when the interrupt controller is not
available:

[    0.153168] irq: no irq domain found for /ap806/config-space@f0000000/interrupt-controller@3f0100 !
[    0.154041] irq: no irq domain found for /cp110-master/config-space@f2000000/interrupt-controller@1e0000 !
[    0.154124] irq: no irq domain found for /cp110-master/config-space@f2000000/interrupt-controller@1e0000 !
[    0.154207] irq: no irq domain found for /cp110-master/config-space@f2000000/interrupt-controller@1e0000 !
[    0.154437] irq: no irq domain found for /cp110-master/config-space@f2000000/interrupt-controller@1e0000 !
[    0.154518] irq: no irq domain found for /cp110-master/config-space@f2000000/interrupt-controller@1e0000 !

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/irq.c

@@ -369,7 +369,10 @@ EXPORT_SYMBOL_GPL(of_irq_parse_one);
  */
 int of_irq_to_resource(struct device_node *dev, int index, struct resource *r)
 {
-	int irq = irq_of_parse_and_map(dev, index);
+	int irq = of_irq_get(dev, index);
+
+	if (irq < 0)
+		return irq;
 
 	/* Only dereference the resource if both the
 	 * resource and the irq are valid. */