[PATCH] dummy-irq: introduce a dummy IRQ handler driver (was Re: gm45 intel gfx can generate non-MSI irq# in MSI mode (was Re: [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt respo))

[Jiri Kosina]

On Wed, 20 Mar 2013, Alan Stern wrote:

> > Ok, so how about this?
> > Daniel, is it enough to make the problem appear on your system (by 
> > building this into the kernel and booting with dummy-irq.irq=16)?
> > 
> > Thanks.
> > 
> > From: Jiri Kosina <jkosina at suse.cz>
> > Subject: [PATCH] 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 at rowland.harvard.edu>
> > Signed-off-by: Jiri Kosina <jkosina at suse.cz>
> 
> This is just what I was thinking of.  Three extremely minor 
> suggestions...

Thanks Alan. Updated version below.

Greg, willing to merge this simple debugging facility?


From: Jiri Kosina <jkosina at suse.cz>
Subject: [PATCH] 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 at rowland.harvard.edu>
Signed-off-by: Jiri Kosina <jkosina at suse.cz>
---
 drivers/misc/Kconfig     |    8 ++++++
 drivers/misc/Makefile    |    1 +
 drivers/misc/dummy-irq.c |   59 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 68 insertions(+), 0 deletions(-)
 create mode 100644 drivers/misc/dummy-irq.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index e83fdfe..69bb79d 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 35a1463..28ff261 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 0000000..7014167
--- /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");

-- 
Jiri Kosina
SUSE Labs