genirq: Add preflow handler support

sparc64 needs to call a preflow handler on certain interrupts befor
calling the action chain. Integrate it into handle_fasteoi_irq. Must
be enabled via CONFIG_IRQ_FASTEOI_PREFLOW. No impact when disabled.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: David S. Miller <davem@davemloft.net>

include/linux/irq.h

@@ -29,9 +29,10 @@
 #include <asm/irq_regs.h>
 
 struct irq_desc;
+struct irq_data;
 typedef	void (*irq_flow_handler_t)(unsigned int irq,
 					    struct irq_desc *desc);
-
+typedef	void (*irq_preflow_handler_t)(struct irq_data *data);
 
 /*
  * IRQ line status.

include/linux/irqdesc.h

@@ -63,6 +63,9 @@ struct irq_desc {
 	struct timer_rand_state *timer_rand_state;
 	unsigned int __percpu	*kstat_irqs;
 	irq_flow_handler_t	handle_irq;
+#ifdef CONFIG_IRQ_PREFLOW_FASTEOI
+	irq_preflow_handler_t	preflow_handler;
+#endif
 	struct irqaction	*action;	/* IRQ action list */
 #ifdef CONFIG_GENERIC_HARDIRQS_NO_COMPAT
 	unsigned int		status_use_accessors;
@@ -187,6 +190,17 @@ static inline void __set_irq_handler_unlocked(int irq,
 	desc = irq_to_desc(irq);
 	desc->handle_irq = handler;
 }
+
+#ifdef CONFIG_IRQ_PREFLOW_FASTEOI
+static inline void
+__irq_set_preflow_handler(unsigned int irq, irq_preflow_handler_t handler)
+{
+	struct irq_desc *desc;
+
+	desc = irq_to_desc(irq);
+	desc->preflow_handler = handler;
+}
+#endif
 #endif
 
 #endif

kernel/irq/Kconfig

@@ -35,6 +35,9 @@ config AUTO_IRQ_AFFINITY
 config HARDIRQS_SW_RESEND
        def_bool n
 
+config IRQ_PREFLOW_FASTEOI
+       def_bool n
+
 config SPARSE_IRQ
 	bool "Support sparse irq numbering"
 	depends on HAVE_SPARSE_IRQ

kernel/irq/chip.c

@@ -471,6 +471,16 @@ handle_level_irq(unsigned int irq, struct irq_desc *desc)
 }
 EXPORT_SYMBOL_GPL(handle_level_irq);
 
+#ifdef CONFIG_IRQ_PREFLOW_FASTEOI
+static inline void preflow_handler(struct irq_desc *desc)
+{
+	if (desc->preflow_handler)
+		desc->preflow_handler(&desc->irq_data);
+}
+#else
+static inline void preflow_handler(struct irq_desc *desc) { }
+#endif
+
 /**
  *	handle_fasteoi_irq - irq handler for transparent controllers
  *	@irq:	the interrupt number
@@ -503,6 +513,7 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc)
 		mask_irq(desc);
 		goto out;
 	}
+	preflow_handler(desc);
 	handle_irq_event(desc);
 out:
 	desc->irq_data.chip->irq_eoi(&desc->irq_data);