genirq: Add internal state field to irq_desc

That field will contain internal state information which is not going
to be exposed to anything outside the core code - except via accessor
functions. I'm tired of everyone fiddling in irq_desc.status.

core_internal_state__do_not_mess_with_it is clear enough, annoying to
type and easy to grep for. Offenders will be tracked down and slapped
with stinking trouts.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/linux/irqdesc.h

@@ -19,6 +19,7 @@ struct timer_rand_state;
  * @handle_irq:		highlevel irq-events handler [if NULL, __do_IRQ()]
  * @action:		the irq action chain
  * @status:		status information
+ * @core_internal_state__do_not_mess_with_it: core internal status information
  * @depth:		disable-depth, for nested irq_disable() calls
  * @wake_depth:		enable depth, for multiple set_irq_wake() callers
  * @irq_count:		stats field to detect stalled irqs
@@ -63,7 +64,7 @@ struct irq_desc {
 	irq_flow_handler_t	handle_irq;
 	struct irqaction	*action;	/* IRQ action list */
 	unsigned int		status;		/* IRQ status */
-
+	unsigned int		core_internal_state__do_not_mess_with_it;
 	unsigned int		depth;		/* nested irq disables */
 	unsigned int		wake_depth;	/* nested wake enables */
 	unsigned int		irq_count;	/* For detecting broken IRQs */

kernel/irq/internals.h

 /*
  * IRQ subsystem internal functions and variables:
+ *
+ * Do not ever include this file from anything else than
+ * kernel/irq/. Do not even think about using any information outside
+ * of this file for your non core code.
  */
 #include <linux/irqdesc.h>
 
@@ -9,6 +13,8 @@
 # define IRQ_BITMAP_BITS	NR_IRQS
 #endif
 
+#define istate core_internal_state__do_not_mess_with_it
+
 extern int noirqdebug;
 
 /*