/* Necessary includes for device drivers */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <asm/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_from/to_user */
#include <linux/ioport.h> /* request_region */
#include <asm/io.h> /* ioremap */
#include <linux/ioctl.h> /* .ioctl fops */

#include "gpio.h"
#define DEVICE_NAME "gpio"

MODULE_LICENSE("DUAL BSD/GPL");

/* Declaration of functions */
int gpio_init(void);
void gpio_exit(void);

// These 4 don't do anything for now
int gpio_open(struct inode *inode, struct file *filp);
int gpio_release(struct inode *inode, struct file *filp);
ssize_t gpio_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t gpio_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos);

// User commands to kernel module
long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg);

// Toggles the the GPIO pin
void gpio_toggle(struct file *filp);

// File operations, has unlocked_ioctl
struct file_operations gpio_fops = {
	.read = gpio_read,
	.write = gpio_write,
	.unlocked_ioctl = gpio_ioctl,
	.open = gpio_open,
	.release = gpio_release
};

/* Global variables of the driver */
#define MMAP_OFFSET 0x44c00000
#define MMAP_SIZE   (0x48ffffff-MMAP_OFFSET)
#define GPIO_PIN_SW 38  // GPIO1.6, Beaglebone P8.3
static void *baseAddr;
static void *gpioSetAddr;
static void *gpioClearAddr;
static void *directionAddr;

/* The major / magic number used can look at 
/linux-3.2.23/Documentation/ioctl/ioctl-number.txt
to find a non-conflicting number */
int gpio_major = 60;

/* Declaration of the init and exit functions */
module_init(gpio_init);
module_exit(gpio_exit);


//Initialize the pointers and register char device
int gpio_init(void)
{
  printk("<1>Init module");
 
  int result;
  // register the char device
  result = register_chrdev(gpio_major, "gpio", &gpio_fops);
  if (result < 0) {
	  printk("<1>gpio: cannot obtain major number %d\n", gpio_major);
	  return result;
  }
  
  // gpio_export(pin);

  // setup_gpio_mem_map();
  baseAddr = ioremap(MMAP_OFFSET, MMAP_SIZE);

  // GPIO configuration
  // if (DEBUG) printf ("Map GPIO\n");

  gpioSetAddr = baseAddr + (0x4804c194 - MMAP_OFFSET);
  gpioClearAddr = baseAddr + (0x4804c190 - MMAP_OFFSET);
  directionAddr = baseAddr + (0x4804c134 - MMAP_OFFSET);
  
	// Set GPIO38 Pin to OUTPUT (drive data)
	*((volatile unsigned int *)directionAddr) &= 0xffffffbf;

	return 0;
}

int gpio_open(struct inode *inode, struct file *filp) {
	return 0;
}

int gpio_release(struct inode *inode, struct file *filp) {
	return 0;
}

ssize_t gpio_read(struct file *filp, char *buf, size_t count, loff_t *f_pos) {
	return 1;
}

ssize_t gpio_write(struct file *filp, const char *buf, size_t count, loff_t *f_pos) {
	return 1;
}

// The code used before to access through the ioremap
void gpio_toggle(struct file *filp) {

	int k;
	for (k = 0; k < 20000000; k++) {
		*((volatile unsigned int *)gpioSetAddr) = 0x40;
		*((volatile unsigned int *)gpioClearAddr) = 0x40;
	}
}

void gpio_exit(void) {
	// gpio_unexport(pin);

	// unmap the ioremap
	iounmap(baseAddr);

	// unregister the char device
	unregister_chrdev(gpio_major, "gpio");

	printk("<1>Removed module");
}

/* 
filp is a pointer to the file, cmd is the command desired
arg is the variable of arguments you pass. It can be a pointer address
How these commands are set up are in gpio.h
*/
long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{

	switch (cmd) {
		// Toggle the GPIO
	case IOC_TOGGLE:
		gpio_toggle(filp);
		break;

		// Read from user (User writes to Kernel)
	case IOC_SET:
		gpio_write(filp, (char *) arg, 1, 0);
		break;

		// Write to user (User reads from Kernel)
	case IOC_GET:
		gpio_read(filp, (char *) arg, 1, 0);
		break;

	default:
		return -ENOTTY;
	}
	return 1;
}