of: irq: fix of_irq_get[_byname]() kernel-doc

The kernel-doc for the of_irq_get[_byname]()  is clearly inadequate in
describing the return values -- of_irq_get_byname() is documented better
than of_irq_get() but it  still doesn't mention that 0 is returned iff
irq_create_of_mapping() fails (it doesn't return an error code in this
case). Document all possible return value variants, making the writing
of the word "IRQ" consistent, while at it...

Fixes: 9ec36caf ("of/irq: do irq resolution in platform_get_irq")
Fixes: ad69674e ("of/irq: do irq resolution in platform_get_irq_byname()")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
CC: stable@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/irq.c

@@ -386,13 +386,13 @@ int of_irq_to_resource(struct device_node *dev, int index, struct resource *r)
 EXPORT_SYMBOL_GPL(of_irq_to_resource);
 
 /**
- * of_irq_get - Decode a node's IRQ and return it as a Linux irq number
+ * of_irq_get - Decode a node's IRQ and return it as a Linux IRQ number
  * @dev: pointer to device tree node
- * @index: zero-based index of the irq
- *
- * Returns Linux irq number on success, or -EPROBE_DEFER if the irq domain
- * is not yet created.
+ * @index: zero-based index of the IRQ
  *
+ * Returns Linux IRQ number on success, or 0 on the IRQ mapping failure, or
+ * -EPROBE_DEFER if the IRQ domain is not yet created, or error code in case
+ * of any other failure.
  */
 int of_irq_get(struct device_node *dev, int index)
 {
@@ -413,12 +413,13 @@ int of_irq_get(struct device_node *dev, int index)
 EXPORT_SYMBOL_GPL(of_irq_get);
 
 /**
- * of_irq_get_byname - Decode a node's IRQ and return it as a Linux irq number
+ * of_irq_get_byname - Decode a node's IRQ and return it as a Linux IRQ number
  * @dev: pointer to device tree node
- * @name: irq name
+ * @name: IRQ name
  *
- * Returns Linux irq number on success, or -EPROBE_DEFER if the irq domain
- * is not yet created, or error code in case of any other failure.
+ * Returns Linux IRQ number on success, or 0 on the IRQ mapping failure, or
+ * -EPROBE_DEFER if the IRQ domain is not yet created, or error code in case
+ * of any other failure.
  */
 int of_irq_get_byname(struct device_node *dev, const char *name)
 {