#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#include <linux/ioctl.h>
#include <asm/gpio.h>

MODULE_LICENSE("GPL");

// Major number
int gpio_major = 70;

// Buffer to store data
char *gpio_buffer;


/* declare local functions */
static int user_gpio_open (struct inode *inode, struct file *filp);
static int user_gpio_release (struct inode *inode, struct file *filp);
static int user_gpio_write_value( struct file *filp, char *buf, size_t count);
static int user_gpio_read_value( struct file *filp, char *buf, size_t count);
static void __exit GIO32_exit(void);
static int  __init GIO32_init(void);

/* declare file operation structure */
static struct file_operations user_gpio_fops = {
    .owner = THIS_MODULE,
    .open  = user_gpio_open,
    .read  = user_gpio_read_value,
    .write = user_gpio_write_value,
    .release = user_gpio_release,
};
//*****************************************************************************
static int __init GIO32_init(void)
{
    int result, result1, result2, result3, result4;
    result = register_chrdev(gpio_major, "PA4", &user_gpio_fops);
    if (result < 0)
    {
        return -1;
    }
    // Allocating memory for the buffer
    gpio_buffer = kmalloc(2, GFP_KERNEL);
    if (!gpio_buffer)
    {
        result = -ENOMEM;
        goto fail;
    }
    memset(gpio_buffer, 0, 2);
    return 0;
    fail:
         GIO32_exit();
         return result;
    return 0;
}

static void __exit GIO32_exit(void)
{
    // Freeing the major number
    unregister_chrdev(gpio_major, "PA4");    
    // Freeing buffer memory
    if (gpio_buffer)
    {
        kfree(gpio_buffer);
    }
}

/* init and exit functions */
module_init(GIO32_init);
module_exit(GIO32_exit);

/ *****************************************************************************/
static int user_gpio_open (struct inode *inode, struct file *filp)
{
    gpio_direction_output(AT91_PIN_PA4,1);
    return 0;
}

/******************************************************************************
 * user_gpio_release - do nothing
 *****************************************************************************/
static int user_gpio_release (struct inode *inode, struct file *filp)
{
    return 0;
}
//******************************************************************************
static int user_gpio_write_value( struct file *filp, char *buf, size_t count)

{
    char *tmp;
    tmp = buf + count - 1;
    copy_from_user(gpio_buffer, tmp, 1);
    if (gpio_buffer[0] == 0)
    {
        gpio_set_value(AT91_PIN_PA4, 0);
    }
    else if (gpio_buffer[0] == 1)
    {
        gpio_direction_output(AT91_PIN_PA4,1);
        gpio_set_value(AT91_PIN_PA4, 1);
    }
    return 1;
}
//******************************************************************************
static int user_gpio_read_value( struct file *filp, char *buf, size_t count)
{
    int val;
    gpio_buffer[0] = gpio_get_value(AT91_PIN_PA4);
    gpio_buffer[1] = gpio_get_value(AT91_PIN_PA4);
    copy_to_user(buf, gpio_buffer, 2);
    return val;
}

fd =  open("/dev/PA4", O_RDWR);
result = read (fd, buf, 2);
И так далее

import os
dev=os.open('/dev/PA4', os.O_RDONLY) - тут все вроде нормально

byte=os.read(dev,2)
File "<stdin>", line 1, in <module>                                           
OSError: [Errno 0] Error

dev = open('/dev/PA4')
byte = dev.read(2)