26.3.4.2内核下的I2C驱动（一）

嵌入式与Linux那些事

发布于 2021-05-20 15:47:16

1.1K0

发布于 2021-05-20 15:47:16

文章被收录于专栏：嵌入式与Linux那些事嵌入式与Linux那些事

1.硬件协议

1.1mini2440 I2C设备如图所示

1.2 I2C协议如下：

1.3启动和停止信号如下图

1.4 I2C总线数据传输时序：

1.5 2440只负责发送，不知道数据含义，只有外设知道。如何写一个字节？参考AT24CXX手册。

注意：I2C设备读之前先写！

2.软件框架

2.1总线-设备-驱动模型如下图所示

把某个结构体，左右的放入链表，一一比较，匹配调用probe函数设备链表 driver链表，总线提供了match函数

linux-2.6.22.6\Documentation\i2c\instantiating-devices

2.2如何构造I2C_CLIENT？设备的4种构建方法

2.1方法一：

mach-mini2440.c

static struct i2c_board_info mini2440_i2c_devs[] __initdata = {
	{
		I2C_BOARD_INFO("24c08", 0x50),//名字：24c08 地址：0x50。知道名字就注册进去，知道地址就知道访问谁
		.platform_data = &at24c08,
	},
};

	i2c_register_board_info(0, mini2440_i2c_devs,
				ARRAY_SIZE(mini2440_i2c_devs));//注册结构体

进入i2c_register_board_info

i2c_register_board_info(int busnum,
	struct i2c_board_info const *info, unsigned len)
{
	int status;

	down_write(&__i2c_board_lock);

	/* dynamic bus numbers will be assigned after the last static one */
	if (busnum >= __i2c_first_dynamic_bus_num)
		__i2c_first_dynamic_bus_num = busnum + 1;

	for (status = 0; len; len--, info++) {
		struct i2c_devinfo	*devinfo;

		devinfo = kzalloc(sizeof(*devinfo), GFP_KERNEL);
		if (!devinfo) {
			pr_debug("i2c-core: can't register boardinfo!\n");
			status = -ENOMEM;
			break;
		}

		devinfo->busnum = busnum;
		devinfo->board_info = *info;
		list_add_tail(&devinfo->list, &__i2c_board_list);//i2c_register_board_info结构体放入链表
	}

	up_write(&__i2c_board_lock);

	return status;
}

什么时候调用链表呢？ i2c-core.c

static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
{
	struct i2c_devinfo	*devinfo;

	down_read(&__i2c_board_lock);
	list_for_each_entry(devinfo, &__i2c_board_list, list) {//链表里面的每一个成员调用i2c_new_device，构造I2C_CLIENT
		if (devinfo->busnum == adapter->nr
				&& !i2c_new_device(adapter,
						&devinfo->board_info))
			dev_err(&adapter->dev,
				"Can't create device at 0x%02x\n",
				devinfo->board_info.addr);
	}
	up_read(&__i2c_board_lock);
}

i2c_new_device.c

i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info)
{
	struct i2c_client	*client;//定义client
	int			status;

	client = kzalloc(sizeof *client, GFP_KERNEL);
	if (!client)
		return NULL;

	client->adapter = adap;

	client->dev.platform_data = info->platform_data;

	if (info->archdata)
		client->dev.archdata = *info->archdata;

	client->flags = info->flags;
	client->addr = info->addr;
	client->irq = info->irq;

	strlcpy(client->name, info->type, sizeof(client->name));

	/* Check for address validity */
	status = i2c_check_client_addr_validity(client);
	if (status) {
		dev_err(&adap->dev, "Invalid %d-bit I2C address 0x%02hx\n",
			client->flags & I2C_CLIENT_TEN ? 10 : 7, client->addr);
		goto out_err_silent;
	}

	/* Check for address business */
	status = i2c_check_addr_busy(adap, client->addr);
	if (status)
		goto out_err;
	/*设置*/
	client->dev.parent = &client->adapter->dev;
	client->dev.bus = &i2c_bus_type;
	client->dev.type = &i2c_client_type;
	client->dev.of_node = info->of_node;

	/* For 10-bit clients, add an arbitrary offset to avoid collisions */
	dev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap),
		     client->addr | ((client->flags & I2C_CLIENT_TEN)
				     ? 0xa000 : 0));
	status = device_register(&client->dev);//注册
	if (status)
		goto out_err;

	dev_dbg(&adap->dev, "client [%s] registered with bus id %s\n",
		client->name, dev_name(&client->dev));

	return client;

out_err:
	dev_err(&adap->dev, "Failed to register i2c client %s at 0x%02x "
		"(%d)\n", client->name, client->addr, status);
out_err_silent:
	kfree(client);
	return NULL;
}

使用限制：必须在 i2c_register_adapter 之前 i2c_register_board_info 所以：不适合我们动态加载insmod

2.2方法二：直接i2c_new_device, i2c_new_probed_device

i2c_new_device, i2c_new_probed_device有什么区别呢？写代码测试下 At24cxx_dev.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/i2c.h>
#include <linux/err.h>
#include <linux/regmap.h>
#include <linux/slab.h>


static struct i2c_board_info at24cxx_info = {	
	I2C_BOARD_INFO("at24c08", 0x50),//芯片手册 1010000
};

static struct i2c_client *at24cxx_client;

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

	i2c_adap = i2c_get_adapter(0);//获得适配器
	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");

At24cxx_drv.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/i2c.h>
#include <linux/err.h>
#include <linux/regmap.h>
#include <linux/slab.h>


static int __devinit at24cxx_probe(struct i2c_client *client,
				  const struct i2c_device_id *id)
{
	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
	return 0;
}

static int __devexit at24cxx_remove(struct i2c_client *client)
{
	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
	return 0;
}

static const struct i2c_device_id at24cxx_id_table[] = {
	{ "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");

编译安装驱动之后，可以正常识别。

将地址改为0X60后，仍然能正常识别

二者区别为： i2c_new_device : 认为设备肯定存在 _new_probed_device ：对于"已经识别出来的设备"(probed_device)，才会创建(“new”) i2c_new_probed_device调用： probe(adap, addr_list[i]) /* 确定设备是否真实存在 */ info->addr = addr_list[i]; i2c_new_device(adap, info);

2.3 第三种从用户空间实例化

实例化过程： 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 测试: 删除左边的devices，只留下右边的driver

2.4第四种从I2C总线上分辨出某个设备

前面的3种方法都要事先确定适配器(I2C总线,I2C控制器) 如果我事先并不知道这个I2C设备在哪个适配器上，怎么办？去class表示的所有的适配器上查找如果适配器上一些I2C设备的地址是一样，怎么继续分辨它是哪一款？用detect函数

static struct i2c_driver at24cxx_driver = {
	.class  = I2C_CLASS_HWMON, /* 表示去哪些适配器上找设备 */
	.driver	= {
		.name	= "100ask",
		.owner	= THIS_MODULE,
	},
	.probe		= at24cxx_probe,
	.remove		= __devexit_p(at24cxx_remove),
	.id_table	= at24cxx_id_table,
	.detect     = at24cxx_detect,  /* 用这个函数来检测设备确实存在 */
	.address_list	= addr_list,   /* 这些设备的地址 */
};

去"class表示的这一类"I2C适配器，用"detect函数"来确定能否找到"address_list里的设备", 如果能找到就调用i2c_new_device来注册i2c_client, 这会和i2c_driver的id_table比较，如果匹配，调用probe

At24cxx.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/i2c.h>
#include <linux/err.h>
#include <linux/regmap.h>
#include <linux/slab.h>


static int __devinit at24cxx_probe(struct i2c_client *client,
				  const struct i2c_device_id *id)
{
	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
	return 0;
}

static int __devexit at24cxx_remove(struct i2c_client *client)
{
	printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);
	return 0;
}

static const struct i2c_device_id at24cxx_id_table[] = {
	{ "at24c08", 0 },
	{}
};

static int at24cxx_detect(struct i2c_client *client,
		       struct i2c_board_info *info)
{
	/* 能运行到这里, 表示该addr的设备是存在的
	 * 但是有些设备单凭地址无法分辨(A芯片的地址是0x50, B芯片的地址也是0x50)
	 * 还需要进一步读写I2C设备来分辨是哪款芯片
	 * detect就是用来进一步分辨这个芯片是哪一款，并且设置info->type
	 */
	
	printk("at24cxx_detect : addr = 0x%x\n", client->addr);

	/* 进一步判断是哪一款 */
	
	strlcpy(info->type, "at24c08", I2C_NAME_SIZE);
	return 0;
}

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

/* 1. 分配/设置i2c_driver */
static struct i2c_driver at24cxx_driver = {
	.class  = I2C_CLASS_HWMON, /* 表示去哪些适配器上找设备 */
	.driver	= {
		.name	= "100ask",
		.owner	= THIS_MODULE,
	},
	.probe		= at24cxx_probe,
	.remove		= __devexit_p(at24cxx_remove),
	.id_table	= at24cxx_id_table,
	.detect     = at24cxx_detect,  /* 用这个函数来检测设备确实存在 */
	.address_list	= addr_list,   /* 这些设备的地址 */
};

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");

probe函数被调用，证明左边devices和右边driver中设备名字相同。我们想搞清楚整个过程，必须分析i2c_register_driver过程。下面是程序分析的框架： i2c-core.c.c

i2c_add_driver
	i2c_register_driver
		a. at24cxx_driver放入i2c_bus_type的drv链表
		   并且从dev链表里取出能匹配的i2c_client并调用probe
		driver_register
			
		
		b. 对于每一个适 配器，调用__process_new_driver
		   对于每一个适配器，调用它的函数确定address_list里的设备是否存在
		   如果存在，再调用detect进一步确定、设置(因为有些设备地址相同，需要进一步确认，这一类下面的哪一种)，然后i2c_new_device
		/* Walk the adapters that are already present */
		i2c_for_each_dev(driver, __process_new_driver);
			__process_new_driver
				i2c_do_add_adapter
					/* Detect supported devices on that bus, and instantiate them */
					i2c_detect(adap, driver);
						for (i = 0; address_list[i] != I2C_CLIENT_END; i += 1) {
							err = i2c_detect_address(temp_client, driver);
										/* 判断这个设备是否存在：简单的发出S信号确定有ACK */
										if (!i2c_default_probe(adapter, addr))
											return 0;
										
										memset(&info, 0, sizeof(struct i2c_board_info));
										info.addr = addr;	
										
										// 设置info.type
										err = driver->detect(temp_client, &info);
					
										i2c_new_device

3.完善设备驱动程序

At24cxx_drv.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/i2c.h>
#include <linux/err.h>
#include <linux/regmap.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <asm/uaccess.h>


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);//i2c_smbus_read_byte_data 核心层提供的读写函数，和之前写的I2C驱动不太一样 之前是构造了两个i2c_msg来进行读写
	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[] = {
	{ "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");

At24cxx_dev.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/i2c.h>
#include <linux/err.h>
#include <linux/regmap.h>
#include <linux/slab.h>


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");

I2c_test.c

#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;
}

本文参与腾讯云自媒体分享计划，分享自作者个人站点/博客。

原始发表：2020-01-08 ，如有侵权请联系 cloudcommunity@tencent.com 删除

编程算法

本文分享自作者个人站点/博客前往查看

如有侵权，请联系 cloudcommunity@tencent.com 删除。

本文参与腾讯云自媒体分享计划，欢迎热爱写作的你一起参与！

编程算法

登录后参与评论

0 条评论

热度