genirq: Add IRQCHIP_SKIP_SET_WAKE flag

Some irq chips need the irq_set_wake() functionality, but do not
require a irq_set_wake() callback. Instead of forcing an empty
callback to be implemented add a flag which notes this fact. Check for
the flag in set_irq_wake_real() and return success when set.
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Thomas Gleixner <tglx@linutronix.de>

include/linux/irq.h

@@ -336,12 +336,14 @@ struct irq_chip {
  * IRQCHIP_MASK_ON_SUSPEND:	Mask non wake irqs in the suspend path
  * IRQCHIP_ONOFFLINE_ENABLED:	Only call irq_on/off_line callbacks
  *				when irq enabled
+ * IRQCHIP_SKIP_SET_WAKE:	Skip chip.irq_set_wake(), for this irq chip
  */
 enum {
 	IRQCHIP_SET_TYPE_MASKED		= (1 <<  0),
 	IRQCHIP_EOI_IF_HANDLED		= (1 <<  1),
 	IRQCHIP_MASK_ON_SUSPEND		= (1 <<  2),
 	IRQCHIP_ONOFFLINE_ENABLED	= (1 <<  3),
+	IRQCHIP_SKIP_SET_WAKE		= (1 <<  4),
 };
 
 /* This include will go away once we isolated irq_desc usage to core code */

kernel/irq/manage.c

@@ -467,6 +467,9 @@ static int set_irq_wake_real(unsigned int irq, unsigned int on)
 	struct irq_desc *desc = irq_to_desc(irq);
 	int ret = -ENXIO;
 
+	if (irq_desc_get_chip(desc)->flags &  IRQCHIP_SKIP_SET_WAKE)
+		return 0;
+
 	if (desc->irq_data.chip->irq_set_wake)
 		ret = desc->irq_data.chip->irq_set_wake(&desc->irq_data, on);