code:

#include <linux/kernel.h>  
#include <linux/module.h>  
#include <linux/cdev.h>  
#include <linux/fs.h>  
#include <linux/device.h>  
#include <linux/syscalls.h>
#include <linux/interrupt.h> 
#include <linux/gpio.h>
#include <linux/of_gpio.h>
#include <linux/of_platform.h>
#include <linux/uaccess.h>  
#include <linux/string.h> 

#include <mach/gpio.h>
#include <mach/irqs.h>

#define GPIO_TO_PIN(bank, gpio) (32 * (bank) + (gpio))


struct fpga_key_dev  
{  
    struct cdev cdev;  
    dev_t devno;  
    char test[20];
    struct class *fpga_key_class; 
	struct fasync_struct *async_queue;

	int message_cdev_open;
};  

irqreturn_t irq_handler(int irqno, void *dev_id)

{
	printk("fpga key down\n");

	return IRQ_HANDLED;
}

static int fpga_key_open(struct inode *node, struct file *fd)  
{  
	struct fpga_key_dev *dev;
	
	printk("fpga_key_open()++\n");  

	printk("node->i_cdev = %x\n", (unsigned int)node->i_cdev);
	dev = container_of(node->i_cdev, struct fpga_key_dev, cdev);
	printk("dev->cdev = %x\n", (unsigned int)&dev->cdev);
	printk("dev = %x\n", (unsigned int)dev);
	
	if (!dev->message_cdev_open) {
		dev->message_cdev_open = 1;
		fd->private_data = dev;
	}
	else{
		return -EFAULT;
	}
	
	printk("test[20] = %s\n",dev->test);
	
    printk("fpga_key_open()--\n");  
  
    return 0;  
}   
  
static ssize_t fpga_key_write(struct file *fd, const char __user *buf, size_t len, loff_t *ptr)  
{  
    char temp_buffer [20];  
    int print_size = 0;  
	struct fpga_key_dev *dev = fd->private_data;
      
    printk("fpga_key_wirte()++\n");  
    if(len > 20)  
        print_size = 20;  
    else  
        print_size = len;  
    printk("print_size = %d; len = %d\n", print_size, len);  
    if(copy_from_user(temp_buffer, buf, print_size))  
        return -EFAULT;  

	if (dev->async_queue)
		kill_fasync(&dev->async_queue, SIGIO, POLL_IN); 
	  
    printk("writing data:%s", temp_buffer);  
      
    printk("fpga_key_wirte()--\n");  
  
    return print_size;  
}  
static ssize_t fpga_key_read(struct file *fd, char __user *buf, size_t len, loff_t *ptr)  
{  
      char *temp_buffer = "Hello fpga_key_read !\n";  
      int print_size = 0;  
        
    printk("fpga_key_read()++\n");  
      
    if(len > strnlen(temp_buffer,20))  
        print_size = strnlen(temp_buffer,20);  
    else  
        print_size = len;  
    printk("print_size = %d; len = %d\n", print_size, len);  
    if(copy_to_user(buf, temp_buffer, print_size))  
        return -EFAULT;  
    printk("%s", temp_buffer);  
    printk("fpga_key_read()--\n");  
  
    return print_size;  
}  

static int fpga_key_fasync(int fd, struct file *filp, int mode)
{
	struct fpga_key_dev		*dev = filp->private_data;

	printk("fpga_key_fasync()++\n");
	
	fasync_helper(fd, filp, mode, &dev->async_queue); 

	printk("fpga_key_fasync()--\n");
	
	return 0;
}

static int fpga_key_release(struct inode *node, struct file *fd)  
{  
	struct fpga_key_dev *dev = fd->private_data;
	
	printk("fpga_key_release()++\n"); 

	dev->message_cdev_open = 0;
	fpga_key_fasync(-1, fd, 0);
	
    printk("fpga_key_release()--\n");  
    return 0;  
} 


struct file_operations meassage_operatons =  
{  
    .owner = THIS_MODULE,  
    .open = fpga_key_open,  
    .write = fpga_key_write,
    .read = fpga_key_read, 
    .fasync = fpga_key_fasync,
    .release = fpga_key_release,  
};  
  
struct fpga_key_dev fpga_key_dev;  
static int __init fpga_key_init(void)  
{  
    struct fpga_key_dev * dev;  
	char * temp_char = "hello world\n";
	int ret = 0;
	int inter = 0;
  
    printk("fpga_key_to_app_init