i2c体系结构篇(dev与core层交互)

来源：互联网发布：电脑加密软件编辑：程序博客网时间：2024/05/20 17:24

[本文导读]:I2C总线作为系统总线，广泛用于e2prom,rtc等设备接口中。本文以mpc8309为架构，linux-2.26.34源码为例分析I2C总线的实现过程。

1. I2c-dev.c驱动的结构

如上图所示，I2c-dev.c是实现I2c通用的slave端的通用驱动架构。i2cdev_fops是实现client的文件操作结构.下面首先看一下i2c_driver结构如下:

struct i2c_driver {

unsigned int class;

int (*attach_adapter)(struct i2c_adapter *);

int (*detach_adapter)(struct i2c_adapter *);

int (*probe)(struct i2c_client *, const struct i2c_device_id *);

int (*remove)(struct i2c_client *);

void (*shutdown)(struct i2c_client *);

int (*suspend)(struct i2c_client *, pm_message_t mesg);

int (*resume)(struct i2c_client *);

void (*alert)(struct i2c_client *, unsigned int data);

int (*command)(struct i2c_client *client, unsigned int cmd, void *arg);

struct device_driver driver;

const struct i2c_device_id *id_table;

int (*detect)(struct i2c_client *, struct i2c_board_info *);

const unsigned short *address_list;

struct list_head clients;

};

#define to_i2c_driver(d) container_of(d, struct i2c_driver, driver)

从该驱动的数据结构来看，它是client与adapter之间的联系层.

2. 设备驱动端的具体实现

对于设备端，有client结构对其描述:

struct i2c_client {

unsigned short flags; /* div., see below */

unsigned short addr; /* chip address - NOTE: 7bit */

char name[I2C_NAME_SIZE]; /* */

struct i2c_adapter *adapter; /* the adapter we sit on */

struct i2c_driver *driver; /* and our access routines */

struct device dev; /* the device structure */

int irq; /* irq issued by device */

struct list_head detected;

};

2.1 open:

static int i2cdev_open(struct inode *inode, struct file *file)

{

unsigned int minor = iminor(inode); //获取设备的次设备号

struct i2c_client *client;

struct i2c_adapter *adap;

struct i2c_dev *i2c_dev;

i2c_dev = i2c_dev_get_by_minor(minor);

if (!i2c_dev) return -ENODEV;

adap = i2c_get_adapter(i2c_dev->adap->nr);

if (!adap) return -ENODEV;

client = kzalloc(sizeof(*client), GFP_KERNEL);

if (!client) {

i2c_put_adapter(adap);

return -ENOMEM;

}

snprintf(client->name, I2C_NAME_SIZE, "i2c-dev %d", adap->nr);

client->driver = &i2cdev_driver;

client->adapter = adap;

file->private_data = client;

return 0;

}

Open函数通过次设备号(也就是总线的ID)获取adapter,创建client结构(也就是实际的dev设备)与adapter,driver相关联，并设置私有数据到file里。

2.2 Ioctl：

static long i2cdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

{

struct i2c_client *client = (struct i2c_client *)file->private_data;

unsigned long funcs;

dev_dbg(&client->adapter->dev, "ioctl, cmd=0x%02x, arg=0x%02lx\n",

cmd, arg);

switch ( cmd ) {

case I2C_SLAVE:

case I2C_SLAVE_FORCE:

if ((arg > 0x3ff) ||

(((client->flags & I2C_M_TEN) == 0) && arg > 0x7f))

return -EINVAL;

if (cmd == I2C_SLAVE && i2cdev_check_addr(client->adapter, arg))

return -EBUSY;

client->addr = arg;

return 0;

case I2C_TENBIT:

if (arg)

client->flags |= I2C_M_TEN;

else

client->flags &= ~I2C_M_TEN;

return 0;

case I2C_PEC:

if (arg)

client->flags |= I2C_CLIENT_PEC;

else

client->flags &= ~I2C_CLIENT_PEC;

return 0;

case I2C_FUNCS:

funcs = i2c_get_functionality(client->adapter);

return put_user(funcs, (unsigned long __user *)arg);

case I2C_RDWR:

return i2cdev_ioctl_rdrw(client, arg);

case I2C_SMBUS:

return i2cdev_ioctl_smbus(client, arg);

case I2C_RETRIES:

client->adapter->retries = arg;

break;

case I2C_TIMEOUT:

client->adapter->timeout = msecs_to_jiffies(arg * 10);

break;

default:

return -ENOTTY;

}

return 0;

}

i2cdev_ioctl主要设置从设备地址，使能读写，超时和重入次数.这些在用户空间编程中首先要设置然后才能对从设备进行读写工作.好了，关于设备端的操作说到这里就差不多了。

3． client对adapter增添反应在用户空间方式

/* ------------------------------------------------------------------------- */

* The legacy "i2cdev_driver" is used primarily to get notifications when

* I2C adapters are added or removed, so that each one gets an i2c_dev

* and is thus made available to userspace driver code.

static struct class *i2c_dev_class;

static int i2cdev_attach_adapter(struct i2c_adapter *adap)

{

struct i2c_dev *i2c_dev;

int res;

i2c_dev = get_free_i2c_dev(adap);

if (IS_ERR(i2c_dev))

return PTR_ERR(i2c_dev);

/* register this i2c device with the driver core */

i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,

MKDEV(I2C_MAJOR, adap->nr), NULL,

"i2c-%d", adap->nr);

if (IS_ERR(i2c_dev->dev)) {

res = PTR_ERR(i2c_dev->dev);

goto error;

}

res = device_create_file(i2c_dev->dev, &dev_attr_name);

if (res)

goto error_destroy;

pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",

adap->name, adap->nr);

return 0;

error_destroy:

device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));

error:

return_i2c_dev(i2c_dev);

return res;

}

static int i2cdev_detach_adapter(struct i2c_adapter *adap)

{

struct i2c_dev *i2c_dev;

i2c_dev = i2c_dev_get_by_minor(adap->nr);

if (!i2c_dev) /* attach_adapter must have failed */

return 0;

device_remove_file(i2c_dev->dev, &dev_attr_name);

return_i2c_dev(i2c_dev);

device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));

pr_debug("i2c-dev: adapter [%s] unregistered\n", adap->name);

return 0;

}

从这里可以看出，这两个函数主要增加设备节点的功能，使用udev文件系统，动态添加设备节点.因为这是dev角度来写的，所以不存在probe等函数，probe是总线驱动所实现的功能.

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