Raspbery Pi gpio interrupts in kernel space C source code, kernel module

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This code is from project: Raspberry pi gpio interrupts in kernel space

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m_test.c

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>

#include <linux/interrupt.h>
#include <linux/gpio.h>


#define DRIVER_AUTHOR "Igor <hardware.coder@gmail.com>"
#define DRIVER_DESC   "Tnterrupt Test"

// we want GPIO_17 (pin 11 on P5 pinout raspberry pi rev. 2 board)
// to generate interrupt
#define GPIO_ANY_GPIO                17

// text below will be seen in 'cat /proc/interrupt' command
#define GPIO_ANY_GPIO_DESC           "Some gpio pin description"

// below is optional, used in more complex code, in our case, this could be
// NULL
#define GPIO_ANY_GPIO_DEVICE_DESC    "some_device"


/****************************************************************************/
/* Interrupts variables block                                               */
/****************************************************************************/
short int irq_any_gpio    = 0;


/****************************************************************************/
/* IRQ handler - fired on interrupt                                         */
/****************************************************************************/
static irqreturn_t r_irq_handler(int irq, void *dev_id, struct pt_regs *regs) {

   unsigned long flags;
  
   // disable hard interrupts (remember them in flag 'flags')
   local_irq_save(flags);

   // NOTE:
   // Anonymous Sep 17, 2013, 3:16:00 PM:
   // You are putting printk while interupt are disabled. printk can block.
   // It's not a good practice.
   // 
   // hardware.coder:
   // http://stackoverflow.com/questions/8738951/printk-inside-an-interrupt-handler-is-it-really-that-bad

   printk(KERN_NOTICE "Interrupt [%d] for device %s was triggered !.\n",
          irq, (char *) dev_id);

   // restore hard interrupts
   local_irq_restore(flags);

   return IRQ_HANDLED;
}


/****************************************************************************/
/* This function configures interrupts.                                     */
/****************************************************************************/
void r_int_config(void) {

   if (gpio_request(GPIO_ANY_GPIO, GPIO_ANY_GPIO_DESC)) {
      printk("GPIO request faiure: %s\n", GPIO_ANY_GPIO_DESC);
      return;
   }

   if ( (irq_any_gpio = gpio_to_irq(GPIO_ANY_GPIO)) < 0 ) {
      printk("GPIO to IRQ mapping faiure %s\n", GPIO_ANY_GPIO_DESC);
      return;
   }

   printk(KERN_NOTICE "Mapped int %d\n", irq_any_gpio);

   if (request_irq(irq_any_gpio,
                   (irq_handler_t ) r_irq_handler,
                   IRQF_TRIGGER_FALLING,
                   GPIO_ANY_GPIO_DESC,
                   GPIO_ANY_GPIO_DEVICE_DESC)) {
      printk("Irq Request failure\n");
      return;
   }

   return;
}


/****************************************************************************/
/* This function releases interrupts.                                       */
/****************************************************************************/
void r_int_release(void) {

   free_irq(irq_any_gpio, GPIO_ANY_GPIO_DEVICE_DESC);
   gpio_free(GPIO_ANY_GPIO);

   return;
}


/****************************************************************************/
/* Module init / cleanup block.                                             */
/****************************************************************************/
int r_init(void) {

   printk(KERN_NOTICE "Hello !\n");
   r_int_config();

   return 0;
}

void r_cleanup(void) {
   printk(KERN_NOTICE "Goodbye\n");
   r_int_release();

   return;
}


module_init(r_init);
module_exit(r_cleanup);


/****************************************************************************/
/* Module licensing/description block.                                      */
/****************************************************************************/
MODULE_LICENSE("GPL");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);

Makefile

# my optional module name
MODULE=m_test

# this two variables, depends where you have you raspberry kernel source and tools installed

CCPREFIX=/opt/raspberry_pi-kernel/tools/arm-bcm2708/arm-bcm2708-linux-gnueabi/bin/arm-bcm2708-linux-gnueabi-
KERNEL_SRC=/opt/raspberry_pi-kernel/linux


obj-m += ${MODULE}.o

module_upload=${MODULE}.ko

all: clean compile

compile:
    make ARCH=arm CROSS_COMPILE=${CCPREFIX} -C ${KERNEL_SRC} M=$(PWD) modules

clean:
    make -C ${KERNEL_SRC} M=$(PWD) clean


# this just copies a file to raspberry
install:
    scp ${module_upload} pi@raspberry:test/

info:
    modinfo  ${module_upload}