s390/irq: use irq 0

Irq 0 is currently unused on s390. Since there is no reason to
do this start counting at the beginning and gain an additional
irq. Also correctly report the smallest usable irq number for
dynamic allocation.
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/irq.h

 #ifndef _ASM_IRQ_H
 #define _ASM_IRQ_H
 
-#define EXT_INTERRUPT	1
-#define IO_INTERRUPT	2
-#define THIN_INTERRUPT	3
+#define EXT_INTERRUPT	0
+#define IO_INTERRUPT	1
+#define THIN_INTERRUPT	2
 
-#define NR_IRQS_BASE	4
+#define NR_IRQS_BASE	3
 
 #ifdef CONFIG_PCI_NR_MSI
 # define NR_IRQS	(NR_IRQS_BASE + CONFIG_PCI_NR_MSI)
@@ -13,9 +13,6 @@
 # define NR_IRQS	NR_IRQS_BASE
 #endif
 
-/* This number is used when no interrupt has been assigned */
-#define NO_IRQ		0
-
 /* External interruption codes */
 #define EXT_IRQ_INTERRUPT_KEY	0x0040
 #define EXT_IRQ_CLK_COMP	0x1004

arch/s390/kernel/irq.c

@@ -127,13 +127,10 @@ int show_interrupts(struct seq_file *p, void *v)
 		for_each_online_cpu(cpu)
 			seq_printf(p, "CPU%d       ", cpu);
 		seq_putc(p, '\n');
-		goto out;
 	}
 	if (index < NR_IRQS) {
 		if (index >= NR_IRQS_BASE)
 			goto out;
-		/* Adjust index to process irqclass_main_desc array entries */
-		index--;
 		seq_printf(p, "%s: ", irqclass_main_desc[index].name);
 		irq = irqclass_main_desc[index].irq;
 		for_each_online_cpu(cpu)
@@ -158,7 +155,7 @@ int show_interrupts(struct seq_file *p, void *v)
 
 unsigned int arch_dynirq_lower_bound(unsigned int from)
 {
-	return from < THIN_INTERRUPT ? THIN_INTERRUPT : from;
+	return from < NR_IRQS_BASE ? NR_IRQS_BASE : from;
 }
 
 /*