From a7b594b4905828b3bfc36be39d48b5e07a23c8e1 Mon Sep 17 00:00:00 2001
From: Jonathan Corbet <corbet@lwn.net>
Date: Tue, 30 Apr 2013 22:42:33 +0200
Subject: dummy-irq: require the user to specify an IRQ number

Make sure that we let the user know that without specifying IRQ#,
dummy-irq driver is useless.

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/misc/dummy-irq.c b/drivers/misc/dummy-irq.c
index 7014167..c37eeed 100644
--- a/drivers/misc/dummy-irq.c
+++ b/drivers/misc/dummy-irq.c
@@ -19,7 +19,7 @@
 #include <linux/irq.h>
 #include <linux/interrupt.h>
 
-static int irq;
+static int irq = -1;
 
 static irqreturn_t dummy_interrupt(int irq, void *dev_id)
 {
@@ -36,6 +36,10 @@ static irqreturn_t dummy_interrupt(int irq, void *dev_id)
 
 static int __init dummy_irq_init(void)
 {
+	if (irq < 0) {
+		printk(KERN_ERR "dummy-irq: no IRQ given.  Use irq=N\n");
+		return -EIO;
+	}
 	if (request_irq(irq, &dummy_interrupt, IRQF_SHARED, "dummy_irq", &irq)) {
 		printk(KERN_ERR "dummy-irq: cannot register IRQ %d\n", irq);
 		return -EIO;
-- 
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