irq: Add IRQ_TYPE_DEFAULT for use by PIC drivers

This is meant typically to allow a PIC driver's irq domain map() callback
to establish sane defaults for the interrupt (and make sure that the HW
and the irq_desc are in sync as far as the trigger is concerned).

The irq core may not call the set_trigger callback if it thinks the
trigger is already set to the right setting, so we need to ensure new
descriptors are properly synchronized with the hardware.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

include/linux/irq.h

@@ -49,6 +49,12 @@ typedef	void (*irq_preflow_handler_t)(struct irq_data *data);
  * IRQ_TYPE_LEVEL_LOW		- low level triggered
  * IRQ_TYPE_LEVEL_MASK		- Mask to filter out the level bits
  * IRQ_TYPE_SENSE_MASK		- Mask for all the above bits
+ * IRQ_TYPE_DEFAULT		- For use by some PICs to ask irq_set_type
+ *				  to setup the HW to a sane default (used
+ *                                by irqdomain map() callbacks to synchronize
+ *                                the HW state and SW flags for a newly
+ *                                allocated descriptor).
+ *
  * IRQ_TYPE_PROBE		- Special flag for probing in progress
  *
  * Bits which can be modified via irq_set/clear/modify_status_flags()
@@ -77,6 +83,7 @@ enum {
 	IRQ_TYPE_LEVEL_LOW	= 0x00000008,
 	IRQ_TYPE_LEVEL_MASK	= (IRQ_TYPE_LEVEL_LOW | IRQ_TYPE_LEVEL_HIGH),
 	IRQ_TYPE_SENSE_MASK	= 0x0000000f,
+	IRQ_TYPE_DEFAULT	= IRQ_TYPE_SENSE_MASK,
 
 	IRQ_TYPE_PROBE		= 0x00000010,