genirq: irqchip: Add a mask calculation function

Some chips have weird bit mask access patterns instead of the linear
you expect. Allow them to calculate the cached mask themself.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jean-Francois Moine <moinejf@free.fr>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Gregory Clement <gregory.clement@free-electrons.com>
Cc: Gerlando Falauto <gerlando.falauto@keymile.com>
Cc: Rob Landley <rob@landley.net>
Acked-by: Grant Likely <grant.likely@linaro.org>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Link: http://lkml.kernel.org/r/20130506142539.302898834@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/irq.h b/include/linux/irq.h
index d5fc7f5..ab8169f 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -296,6 +296,7 @@
  * @irq_suspend:	function called from core code on suspend once per chip
  * @irq_resume:		function called from core code on resume once per chip
  * @irq_pm_shutdown:	function called from core code on shutdown once per chip
+ * @irq_calc_mask:	Optional function to set irq_data.mask for special cases
  * @irq_print_chip:	optional to print special chip info in show_interrupts
  * @flags:		chip specific flags
  */
@@ -327,6 +328,8 @@
 	void		(*irq_resume)(struct irq_data *data);
 	void		(*irq_pm_shutdown)(struct irq_data *data);
 
+	void		(*irq_calc_mask)(struct irq_data *data);
+
 	void		(*irq_print_chip)(struct irq_data *data, struct seq_file *p);
 
 	unsigned long	flags;