genirq: add unlocked version of set_irq_handler()

Add unlocked version for use by irq_chip.set_type handlers which may
wish to change handler to level or edge handler when IRQ type is
changed.

The normal set_irq_handler() call cannot be used because it tries to
take irq_desc.lock which is already held when the irq_chip.set_type
hook is called.

Signed-off-by: Kevin Hilman <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/irq.h

···
 __set_irq_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
 		  const char *name);
 
+/* caller has locked the irq_desc and both params are valid */
+static inline void __set_irq_handler_unlocked(int irq,
+					      irq_flow_handler_t handler)
+{
+	irq_desc[irq].handle_irq = handler;
+}
+
 /*
  * Set a highlevel flow handler for a given IRQ:
  */