input.c

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

#include <asm/irq.h>
#include <asm/io.h>

static struct input_dev *button_dev;

static irqreturn_t button_interrupt(int irq, void *dummy)
{
        input_report_key(button_dev, BTN_0, inb(BUTTON_PORT) & 1);
        input_sync(button_dev);
        return IRQ_HANDLED;
}

static int __init button_init(void)
{
        int error;

        if (request_irq(BUTTON_IRQ, button_interrupt, 0, "button", NULL)) {
                printk(KERN_ERR "button.c: Can't allocate irq %d\n", button_irq);
                return -EBUSY;
        }

        button_dev = input_allocate_device();
        if (!button_dev) {
                printk(KERN_ERR "button.c: Not enough memory\n");
                error = -ENOMEM;
                goto err_free_irq;
        }

        button_dev->evbit[0] = BIT_MASK(EV_KEY);
        button_dev->keybit[BIT_WORD(BTN_0)] = BIT_MASK(BTN_0);

        error = input_register_device(button_dev);
        if (error) {
                printk(KERN_ERR "button.c: Failed to register device\n");
                goto err_free_dev;
        }

        return 0;

err_free_dev:
        input_free_device(button_dev);
err_free_irq:
        free_irq(BUTTON_IRQ, button_interrupt);
        return error;
}

static void __exit button_exit(void)
{
        input_unregister_device(button_dev);
        free_irq(BUTTON_IRQ, button_interrupt);
}

module_init(button_init);
module_exit(button_exit);