#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/jiffies.h>
#include <linux/i2c.h>
#include <linux/mutex.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

static unsigned short ignore[]      = { I2C_CLIENT_END };
static unsigned short normal_addr[] = { 0x50, I2C_CLIENT_END }; /* 地址值是7位 */
                                        /* 改為0x60的話, 由於不存在裝置地址為0x60的裝置, 所以at24cxx_detect不被呼叫 */

static unsigned short force_addr[] = {ANY_I2C_BUS, 0x60, I2C_CLIENT_END};
static unsigned short * forces[] = {force_addr, NULL};
										
static struct i2c_client_address_data addr_data = {
	.normal_i2c	= normal_addr,  /* 要發出S訊號和裝置地址並得到ACK訊號,才能確定存在這個裝置 */
	.probe		= ignore,
	.ignore		= ignore,
	//.forces     = forces, /* 強制認為存在這個裝置 */
};

static struct i2c_driver at24cxx_driver;


static int major;
static struct class *cls;
struct i2c_client *at24cxx_client;

static ssize_t at24cxx_read(struct file *file, char __user *buf, size_t size, loff_t * offset)
{
	unsigned char address;
	unsigned char data;
	struct i2c_msg msg[2];
	int ret;
	
	/* address = buf[0] 
	 * data    = buf[1]
	 */
	if (size != 1)
		return -EINVAL;
	
	copy_from_user(&address, buf, 1);

	/* 資料傳輸三要素: 源,目的,長度 */

	/* 讀AT24CXX時,要先把要讀的儲存空間的地址發給它 */
	msg[0].addr  = at24cxx_client->addr;  /* 目的 */
	msg[0].buf   = &address;              /* 源 */
	msg[0].len   = 1;                     /* 地址=1 byte */
	msg[0].flags = 0;                     /* 表示寫 */

	/* 然後啟動讀操作 */
	msg[1].addr  = at24cxx_client->addr;  /* 源 */
	msg[1].buf   = &data;                 /* 目的 */
	msg[1].len   = 1;                     /* 資料=1 byte */
	msg[1].flags = I2C_M_RD;                     /* 表示讀 */


	ret = i2c_transfer(at24cxx_client->adapter, msg, 2);
	if (ret == 2)
	{
		copy_to_user(buf, &data, 1);
		return 1;
	}
	else
		return -EIO;
}

static ssize_t at24cxx_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
	unsigned char val[2];
	struct i2c_msg msg[1];
	int ret;
	
	/* address = buf[0] 
	 * data    = buf[1]
	 */
	if (size != 2)
		return -EINVAL;
	
	copy_from_user(val, buf, 2);

	/* 資料傳輸三要素: 源,目的,長度 */
	msg[0].addr  = at24cxx_client->addr;  /* 目的 */
	msg[0].buf   = val;                   /* 源 */
	msg[0].len   = 2;                     /* 地址+資料=2 byte */
	msg[0].flags = 0;                     /* 表示寫 */

	ret = i2c_transfer(at24cxx_client->adapter, msg, 1);
	if (ret == 1)
		return 2;
	else
		return -EIO;
}


static struct file_operations at24cxx_fops = {
	.owner = THIS_MODULE,
	.read  = at24cxx_read,
	.write = at24cxx_write,
};

static int at24cxx_detect(struct i2c_adapter *adapter, int address, int kind)
{	
	printk("at24cxx_detect\n");

	/* 構構一個i2c_client結構體: 以後收改資料時會用到它 */
	at24cxx_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
	at24cxx_client->addr    = address;
	at24cxx_client->adapter = adapter;
	at24cxx_client->driver  = &at24cxx_driver;
	strcpy(at24cxx_client->name, "at24cxx");
	i2c_attach_client(at24cxx_client);
	
	major = register_chrdev(0, "at24cxx", &at24cxx_fops);

	cls = class_create(THIS_MODULE, "at24cxx");
	class_device_create(cls, NULL, MKDEV(major, 0), NULL, "at24cxx"); /* /dev/at24cxx */
	
	return 0;
}

static int at24cxx_attach(struct i2c_adapter *adapter)
{
	return i2c_probe(adapter, &addr_data, at24cxx_detect);
}

static int at24cxx_detach(struct i2c_client *client)
{
	printk("at24cxx_detach\n");
	class_device_destroy(cls, MKDEV(major, 0));
	class_destroy(cls);
	unregister_chrdev(major, "at24cxx");

	i2c_detach_client(client);
	kfree(i2c_get_clientdata(client));

	return 0;
}


/* 1. 分配一個i2c_driver結構體 */
/* 2. 設定i2c_driver結構體 */
static struct i2c_driver at24cxx_driver = {
	.driver = {
		.name	= "at24cxx",
	},
	.attach_adapter = at24cxx_attach,
	.detach_client  = at24cxx_detach,
};

static int at24cxx_init(void)
{
	i2c_add_driver(&at24cxx_driver);
	return 0;
}

static void at24cxx_exit(void)
{
	i2c_del_driver(&at24cxx_driver);
}

module_init(at24cxx_init);
module_exit(at24cxx_exit);

MODULE_LICENSE("GPL");