Simple interrupt handler: request_irq returns error code -22

Question

I am writing a simple kernel module, which could register an interrupt and handle it. However, when I try to register interrupt by calling the request_irq function, it returns error code -22 :

ERROR: Cannot request IRQ 30 - code -22 , EIO 5 , EINVAL 22

I believe, this error code is equal to EINVAL (invalid argument)

Please tell me, what I am doing wrong. Here is a module:

#include <linux/init.h>
#include <linux/module.h>
#include <linux/irq.h>
#include <linux/io.h>
#include <linux/irqdomain.h>
#include <linux/interrupt.h>
#include <linux/of.h>
#include <linux/of_address.h>

#include <asm/exception.h>
#include <asm/mach/irq.h>

void int068_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    printk("Interrupt should be handled there\n");
}

static int __init
clcdint_init(void)
{
    unsigned int irq;
    unsigned int irqflags;
    int ret;

    irq=68;
    irqflags=IRQF_SHARED | IRQF_NO_SUSPEND;

    ret = request_irq(irq, int068_interrupt,
            irqflags, "clcdint-int068", NULL);

    if (ret!=0) {
            printk("ERROR: Cannot request IRQ %d", irq);
            printk(" - code %d , EIO %d , EINVAL %d\n", ret, EIO, EINVAL);
    }

    printk("CLCDINT_INIT\n");
    return 0;
}

module_init(clcdint_init);

static void __exit
clcdint_exit(void)
{
    unsigned int irq;
    irq=68;
    free_irq(irq, NULL);
    printk("CLCDINT_EXIT\n");
}

module_exit(clcdint_exit);

Answer 1

You can't pass a NULL context (last parameters of the request_irq() call) when dealing with a shared interrupt line (IRQF_SHARED flag is on).

To understand why consider the following scenario: you have two identical network cards sharing the same IRQ. The same driver will pass the same interrupt handler function, the same irq number and the same description. There is no way to distinguish the two instances of the registration except via the context parameter.

Therefore, as a precaution, you can't pass a NULL context parameter if you pass the IRQF_SHARED flag.