dummy-irq: introduce a dummy IRQ handler driver

This module accepts a single 'irq' parameter, which it should register for.

Its sole purpose is to help with debugging of IRQ sharing problems, by
force-enabling IRQ that would otherwise be disabled.

Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 68 insertions, 0 deletions

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index e83fdfe0c8ca..69bb79d6dd54 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -93,6 +93,14 @@ config ATMEL_TCB_CLKSRC_BLOCK
           TC can be used for other purposes, such as PWM generation and
           interval timing.
 
+config DUMMY_IRQ
+        tristate "Dummy IRQ handler"
+        default n
+        ---help---
+          This module accepts a single 'irq' parameter, which it should register for.
+          The sole purpose of this module is to help with debugging of systems on
+          which spurious IRQs would happen on disabled IRQ vector.
+
 config IBM_ASM
         tristate "Device driver for IBM RSA service processor"
         depends on X86 && PCI && INPUT
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 3e2faa0939b2..865cbc6a7ae1 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_ATMEL_TCLIB)	+= atmel_tclib.o
 obj-$(CONFIG_BMP085)            += bmp085.o
 obj-$(CONFIG_BMP085_I2C)        += bmp085-i2c.o
 obj-$(CONFIG_BMP085_SPI)        += bmp085-spi.o
+obj-$(CONFIG_DUMMY_IRQ)         += dummy-irq.o
 obj-$(CONFIG_ICS932S401)        += ics932s401.o
 obj-$(CONFIG_LKDTM)             += lkdtm.o
 obj-$(CONFIG_TIFM_CORE)         += tifm_core.o
diff --git a/drivers/misc/dummy-irq.c b/drivers/misc/dummy-irq.c
new file mode 100644
index 000000000000..7014167e2c61
--- /dev/null
+++ b/drivers/misc/dummy-irq.c
@@ -0,0 +1,59 @@
+/*
+ * Dummy IRQ handler driver.
+ *
+ * This module only registers itself as a handler that is specified to it
+ * by the 'irq' parameter.
+ *
+ * The sole purpose of this module is to help with debugging of systems on
+ * which spurious IRQs would happen on disabled IRQ vector.
+ *
+ * Copyright (C) 2013 Jiri Kosina
+ */
+
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ */
+#include <linux/module.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+
+static int irq;
+
+static irqreturn_t dummy_interrupt(int irq, void *dev_id)
+{
+        static int count = 0;
+
+        if (count == 0) {
+                printk(KERN_INFO "dummy-irq: interrupt occured on IRQ %d\n",
+                                irq);
+                count++;
+        }
+
+        return IRQ_NONE;
+}
+
+static int __init dummy_irq_init(void)
+{
+        if (request_irq(irq, &dummy_interrupt, IRQF_SHARED, "dummy_irq", &irq)) {
+                printk(KERN_ERR "dummy-irq: cannot register IRQ %d\n", irq);
+                return -EIO;
+        }
+        printk(KERN_INFO "dummy-irq: registered for IRQ %d\n", irq);
+        return 0;
+}
+
+static void __exit dummy_irq_exit(void)
+{
+        printk(KERN_INFO "dummy-irq unloaded\n");
+        free_irq(irq, &irq);
+}
+
+module_init(dummy_irq_init);
+module_exit(dummy_irq_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jiri Kosina");
+module_param(irq, uint, 0444);
+MODULE_PARM_DESC(irq, "The IRQ to register for");