[PATCH] genirq MSI fixes

This is a fixed up and cleaned up replacement for genirq-msi-fixes.patch,
which should solve the i386 4KSTACKS problem.  I also added Ben's idea of
pushing the __do_IRQ() check into generic_handle_irq().

I booted this with MSI enabled, but i only have MSI devices, not MSI-X
devices.  I'd still expect MSI-X to work now.

irqchip migration helper: call __do_IRQ() if a descriptor is attached to an
irqtype-style controller.  This also fixes MSI-X IRQ handling on i386 and
x86_64.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/irq.c

@@ -82,6 +82,10 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
 	}
 #endif
 
+	if (!irq_desc[irq].handle_irq) {
+		__do_IRQ(irq, regs);
+		goto out_exit;
+	}
 #ifdef CONFIG_4KSTACKS
 
 	curctx = (union irq_ctx *) current_thread_info();
@@ -121,6 +125,7 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
 #endif
 		__do_IRQ(irq, regs);
 
+out_exit:
 	irq_exit();
 
 	return 1;

include/linux/irq.h

@@ -176,17 +176,6 @@ typedef struct irq_desc		irq_desc_t;
  */
 #include <asm/hw_irq.h>
 
-/*
- * Architectures call this to let the generic IRQ layer
- * handle an interrupt:
- */
-static inline void generic_handle_irq(unsigned int irq, struct pt_regs *regs)
-{
-	struct irq_desc *desc = irq_desc + irq;
-
-	desc->handle_irq(irq, desc, regs);
-}
-
 extern int setup_irq(unsigned int irq, struct irqaction *new);
 
 #ifdef CONFIG_GENERIC_HARDIRQS
@@ -324,6 +313,22 @@ handle_irq_name(void fastcall (*handle)(unsigned int, struct irq_desc *,
  */
 extern fastcall unsigned int __do_IRQ(unsigned int irq, struct pt_regs *regs);
 
+/*
+ * Architectures call this to let the generic IRQ layer
+ * handle an interrupt. If the descriptor is attached to an
+ * irqchip-style controller then we call the ->handle_irq() handler,
+ * and it calls __do_IRQ() if it's attached to an irqtype-style controller.
+ */
+static inline void generic_handle_irq(unsigned int irq, struct pt_regs *regs)
+{
+	struct irq_desc *desc = irq_desc + irq;
+
+	if (likely(desc->handle_irq))
+		desc->handle_irq(irq, desc, regs);
+	else
+		__do_IRQ(irq, regs);
+}
+
 /* Handling of unhandled and spurious interrupts: */
 extern void note_interrupt(unsigned int irq, struct irq_desc *desc,
 			   int action_ret, struct pt_regs *regs);