i2c 驱动程序编写

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关于i2c设备的实例化，可参考Documentation\i2c\instantiating-devices，该帮助文档列举了4中 i2c设备的构建方式。

方法1. 定义一个i2c_board_info数组，内部枚举各设备的名字和设备地址，通过i2c_register_board_info(busnum, ...) ；该注册函数将i2c设备信息放入__i2c_board_list链表；当i2c总线注册时会扫描该链表并且自动创建i2c设备；i2c_register_adapter > i2c_scan_static_board_info > i2c_new_device；所以，我们在使用该方法时，应该在i2c_register_adapter 之前i2c_register_board_info，不适合动态加载驱动程序。

Example (from omap2 h4):

static struct i2c_board_info h4_i2c_board_info[] __initdata = {
	{
		I2C_BOARD_INFO("isp1301_omap", 0x2d),
		.irq		= OMAP_GPIO_IRQ(125),
	},
	{	/* EEPROM on mainboard */
		I2C_BOARD_INFO("24c01", 0x52),
		.platform_data	= &m24c01,
	},
	{	/* EEPROM on cpu card */
		I2C_BOARD_INFO("24c01", 0x57),
		.platform_data	= &m24c01,
	},
};

static void __init omap_h4_init(void)
{
	(...)
	i2c_register_board_info(1, h4_i2c_board_info,
			ARRAY_SIZE(h4_i2c_board_info));
	(...)
}

方法2. 显示构建i2c设备；

当我们认为设备肯定存在时，可以直接调用i2c_new_device构建设备。

static struct i2c_board_info at24cxx_info = {	
	I2C_BOARD_INFO("at24c08", 0x50),
};

static struct i2c_client *at24cxx_client;

static int at24cxx_dev_init(void)
{
	struct i2c_adapter *i2c_adap;

	i2c_adap = i2c_get_adapter(0);
	at24cxx_client = i2c_new_device(i2c_adap, &at24cxx_info);
	i2c_put_adapter(i2c_adap);
	
	return 0;
}

static void at24cxx_dev_exit(void)
{
	i2c_unregister_device(at24cxx_client);
}


module_init(at24cxx_dev_init);
module_exit(at24cxx_dev_exit);
MODULE_LICENSE("GPL");

如果我们不确定该总线上存在该设备，我们可以提供一个地址列表，使用i2c_new_probed_device去探测，当探测识别出该设备时才会构建i2c设备。

static struct i2c_client *at24cxx_client;

static const unsigned short addr_list[] = { 0x60, 0x50, I2C_CLIENT_END };

static int at24cxx_dev_init(void)
{
	struct i2c_adapter *i2c_adap;
	struct i2c_board_info at24cxx_info;

	memset(&at24cxx_info, 0, sizeof(struct i2c_board_info));	
	strlcpy(at24cxx_info.type, "at24c08", I2C_NAME_SIZE);

	i2c_adap = i2c_get_adapter(0);
	at24cxx_client = i2c_new_probed_device(i2c_adap, &at24cxx_info, addr_list, NULL);
	i2c_put_adapter(i2c_adap);

	if (at24cxx_client)
		return 0;
	else
		return -ENODEV;
}

static void at24cxx_dev_exit(void)
{
	i2c_unregister_device(at24cxx_client);
}


module_init(at24cxx_dev_init);
module_exit(at24cxx_dev_exit);
MODULE_LICENSE("GPL");

方法3. 从用户空间创建设备

创建设备：echo at24c08 0x50 > /sys/class/i2c-adapter/i2c-0/new_device，导致i2c_new_device被调用
删除设备：echo 0x50 > /sys/class/i2c-adapter/i2c-0/delete_device，导致i2c_unregister_device

方法4. 前面3中方法都要事先确定适配器（i2c总线、i2c控制器），如果我们们事先不知道该i2c设备连接到哪个适配器上怎么办？示例见 drivers/hwmon/lm90.c

驱动程序示例：

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

/* 传入: buf[0] : addr
 * 输出: buf[0] : data
 */
static ssize_t at24cxx_read(struct file * file, char __user *buf, size_t count, loff_t *off)
{
	unsigned char addr, data;
	
	copy_from_user(&addr, buf, 1);
	data = i2c_smbus_read_byte_data(at24cxx_client, addr);
	copy_to_user(buf, &data, 1);
	return 1;
}

/* buf[0] : addr
 * buf[1] : data
 */
static ssize_t at24cxx_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
{
	unsigned char ker_buf[2];
	unsigned char addr, data;

	copy_from_user(ker_buf, buf, 2);
	addr = ker_buf[0];
	data = ker_buf[1];

	printk("addr = 0x%02x, data = 0x%02x\n", addr, data);

	if (!i2c_smbus_write_byte_data(at24cxx_client, addr, data))
		return 2;
	else
		return -EIO;	
}

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

static int __devinit at24cxx_probe(struct i2c_client *client,
				  const struct i2c_device_id *id)
{
	at24cxx_client = client;
		
	//printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
	major = register_chrdev(0, "at24cxx", &at24cxx_fops);
	class = class_create(THIS_MODULE, "at24cxx");
	device_create(class, NULL, MKDEV(major, 0), NULL, "at24cxx"); /* /dev/at24cxx */
	
	return 0;
}

static int __devexit at24cxx_remove(struct i2c_client *client)
{
	//printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
	device_destroy(class, MKDEV(major, 0));
	class_destroy(class);
	unregister_chrdev(major, "at24cxx");
		
	return 0;
}

static const struct i2c_device_id at24cxx_id_table[] = {// name很重要，需要和i2c_board_info中的type匹配
	{ "at24c08", 0 },
	{}
};


/* 1. 分配/设置i2c_driver */
static struct i2c_driver at24cxx_driver = {
	.driver	= {
		.name	= "100ask",
		.owner	= THIS_MODULE,
	},
	.probe		= at24cxx_probe,
	.remove		= __devexit_p(at24cxx_remove),
	.id_table	= at24cxx_id_table,
};

static int at24cxx_drv_init(void)
{
	/* 2. 注册i2c_driver */
	i2c_add_driver(&at24cxx_driver);
	
	return 0;
}

static void at24cxx_drv_exit(void)
{
	i2c_del_driver(&at24cxx_driver);
}


module_init(at24cxx_drv_init);
module_exit(at24cxx_drv_exit);
MODULE_LICENSE("GPL");

驱动测试程序：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


/* i2c_test r addr
 * i2c_test w addr val
 */

void print_usage(char *file)
{
	printf("%s r addr\n", file);
	printf("%s w addr val\n", file);
}

int main(int argc, char **argv)
{
	int fd;
	unsigned char buf[2];
	
	if ((argc != 3) && (argc != 4))
	{
		print_usage(argv[0]);
		return -1;
	}

	fd = open("/dev/at24cxx", O_RDWR);
	if (fd < 0)
	{
		printf("can't open /dev/at24cxx\n");
		return -1;
	}

	if (strcmp(argv[1], "r") == 0)
	{
		buf[0] = strtoul(argv[2], NULL, 0);
		read(fd, buf, 1);
		printf("data: %c, %d, 0x%2x\n", buf[0], buf[0], buf[0]);
	}
	else if ((strcmp(argv[1], "w") == 0) && (argc == 4))
	{
		buf[0] = strtoul(argv[2], NULL, 0);
		buf[1] = strtoul(argv[3], NULL, 0);
		if (write(fd, buf, 2) != 2)
			printf("write err, addr = 0x%02x, data = 0x%02x\n", buf[0], buf[1]);
	}
	else
	{
		print_usage(argv[0]);
		return -1;
	}
	
	return 0;
}