powerpc/irq: Move get_irq() comment into header

The guts of do_IRQ() isn't really the right place to be documenting
the ppc_md.get_irq() interface. So move the comment into machdep.h
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/machdep.h

@@ -110,6 +110,10 @@ struct machdep_calls {
 	void		(*show_percpuinfo)(struct seq_file *m, int i);
 
 	void		(*init_IRQ)(void);
+
+	/* Return an irq, or NO_IRQ to indicate there are none pending.
+	 * If for some reason there is no irq, but the interrupt
+	 * shouldn't be counted as spurious, return NO_IRQ_IGNORE. */
 	unsigned int	(*get_irq)(void);
 #ifdef CONFIG_KEXEC
 	void		(*kexec_cpu_down)(int crash_shutdown, int secondary);

arch/powerpc/kernel/irq.c

@@ -326,13 +326,6 @@ void do_IRQ(struct pt_regs *regs)
 
 	check_stack_overflow();
 
-	/*
-	 * Every platform is required to implement ppc_md.get_irq.
-	 * This function will either return an irq number or NO_IRQ to
-	 * indicate there are no more pending.
-	 * The value NO_IRQ_IGNORE is for buggy hardware and means that this
-	 * IRQ has already been handled. -- Tom
-	 */
 	irq = ppc_md.get_irq();
 
 	if (irq != NO_IRQ && irq != NO_IRQ_IGNORE)