genirq: Add wakeup sysfs node to show IRQ wakeup state

Surprisingly there is no simple way to see if the IRQ line in question
is wakeup source or not.

Note that wakeup might be an OOB (out-of-band) source like GPIO line
which makes things slightly more complicated.

Add a sysfs node to cover this case.

Signed-off-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Tested-by: Tony Lindgren <[e-mail]>
Cc: Grygorii Strashko <[e-mail]>
Cc: "Rafael J . Wysocki" <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

Documentation/ABI/testing/sysfs-kernel-irq

···
 KernelVersion:	4.9
 Contact:	Craig Gallek <[e-mail]>
 Description:	The type of the interrupt.  Either the string 'level' or 'edge'.
+
+What:		/sys/kernel/irq/<irq>/wakeup
+Date:		March 2018
+KernelVersion:	4.17
+Contact:	Andy Shevchenko <[e-mail]>
+Description:	The wakeup state of the interrupt. Either the string
+		'enabled' or 'disabled'.

kernel/irq/irqdesc.c

···
 }
 IRQ_ATTR_RO(type);
 
+static ssize_t wakeup_show(struct kobject *kobj,
+			   struct kobj_attribute *attr, char *buf)
+{
+	struct irq_desc *desc = container_of(kobj, struct irq_desc, kobj);
+	ssize_t ret = 0;
+
+	raw_spin_lock_irq(&desc->lock);
+	ret = sprintf(buf, "%s\n",
+		      irqd_is_wakeup_set(&desc->irq_data) ? "enabled" : "disabled");
+	raw_spin_unlock_irq(&desc->lock);
+
+	return ret;
+
+}
+IRQ_ATTR_RO(wakeup);
+
 static ssize_t name_show(struct kobject *kobj,
 			 struct kobj_attribute *attr, char *buf)
 {
···
 	&chip_name_attr.attr,
 	&hwirq_attr.attr,
 	&type_attr.attr,
+	&wakeup_attr.attr,
 	&name_attr.attr,
 	&actions_attr.attr,
 	NULL