ARM: 6806/1: irq: introduce entry and exit functions for chained handlers

Some chained IRQ handlers are written to cope with primary chips of
potentially different flow types. Whether this a sensible thing to do
is a point of contention.

This patch introduces entry/exit functions for chained handlers which
infer the flow type of the primary chip as fasteoi or level-type by
checking whether or not the ->irq_eoi function pointer is present and
calling back to the primary chip as necessary. Other methods of flow
control are not considered.
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/mach/irq.h

@@ -34,4 +34,35 @@ do {							\
 	raw_spin_unlock(&desc->lock);			\
 } while(0)
 
+#ifndef __ASSEMBLY__
+/*
+ * Entry/exit functions for chained handlers where the primary IRQ chip
+ * may implement either fasteoi or level-trigger flow control.
+ */
+static inline void chained_irq_enter(struct irq_chip *chip,
+				     struct irq_desc *desc)
+{
+	/* FastEOI controllers require no action on entry. */
+	if (chip->irq_eoi)
+		return;
+
+	if (chip->irq_mask_ack) {
+		chip->irq_mask_ack(&desc->irq_data);
+	} else {
+		chip->irq_mask(&desc->irq_data);
+		if (chip->irq_ack)
+			chip->irq_ack(&desc->irq_data);
+	}
+}
+
+static inline void chained_irq_exit(struct irq_chip *chip,
+				    struct irq_desc *desc)
+{
+	if (chip->irq_eoi)
+		chip->irq_eoi(&desc->irq_data);
+	else
+		chip->irq_unmask(&desc->irq_data);
+}
+#endif
+
 #endif