Linux I2C core

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#linux #c语言 #i2c-core #i2c

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本文详细介绍了Linux I2C核心模块(i2c-core.c)的功能，包括I2C适配器和驱动程序的注册与注销、客户端的关联与解除关联，以及I2C数据传输的基本操作。通过具体代码示例展示了这些功能是如何实现的。

Linux I2C core

File path : kernel/driver/i2c/i2c-core.c

I2C bus driver and device driver以I2C core作为核心，i2c-core.c中为bus driver and device driver提供了一组不依赖于硬件平台的接口函数。

(1)增加/删除 i2c_adapter

int i2c_add_adapter(struct i2c_adapter *adap);
int i2c_del_adapter(struct i2c_adapter *adap);

(2)增加/删除 i2c_driver

int i2c_register_driver(struct module *owner, struct *driver);
int i2c_del_driver(struct i2c_driver *driver);
inline int i2c_add_driver(struct i2c_driver *driver);

(3)i2c_client 依附/脱离

int i2c_attach_client(struct i2c_client *client);
int i2c_detach_client(struct i2c_client *client);

当一个具体的client被侦测到并被关联到的时候，设备和sysfs文件将被注册，相反，在client被取消关联的时候，sysfs文件和设备也被注销，从下面的代码所示：

int i2c_attach_client(struct i2c_client *client)
{
    ...
    device_register(&client->dev);
    device_create_file(&client->dev, &dev_attr_client_name);
    return 0;
    }
    int i2c_detach_client(struct i2c_client *client)
    {
    ...
    device_remove_file(&client->dev, &dev_attr_client_name);
    device_unregister(&client->dev);
    ...
}

(4)I2C 传输、发送和接收。

int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num);
int i2c_master_send(struct i2c_client *client,const char *buf ,int count);
int i2c_master_recv(struct i2c_client *client, char *buf ,int count);

i2c_transfer() 函数用于进行 I2C 适配器和 I2C 设备之间的一组消息交互 ,i2c_master_send()函数和 i2c_master_recv()函数内部会调用i2c_transfer()函数分别完成一条写消息和一条读消息，如下代码所示：

int i2c_master_send(struct i2c_client *client,const char *buf ,int count)
{
    int ret;
    struct i2c_adapter *adap=client->adapter;
    struct i2c_msg msg;

    /*构造一个写消息*/
    msg.addr = client->addr;
    msg.flags = client->flags & I2C_M_TEN;
    msg.len = count;
    msg.buf = (char *)buf;

    /*传输消息*/
    ret = i2c_transfer(adap, &msg, 1);

    return (ret == 1) ? count : ret;
}

int i2c_master_recv(struct i2c_client *client, char *buf ,int count)
{
    struct i2c_adapter *adap=client->adapter;
    struct i2c_msg msg;
    int ret;
    /*构造一个读消息*/
    msg.addr = client->addr;
    msg.flags = client->flags & I2C_M_TEN;
    msg.flags |= I2C_M_RD;
    msg.len = count;
    msg.buf = buf;
    /*传输消息*/

    ret = i2c_transfer(adap, &msg, 1);

    /* 成功(1 条消息被处理), 返回读的字节数 */
    return (ret == 1) ? count : ret;
}

i2c_transfer()函数本身不具备驱动适配器物理硬件完成消息交互的能力,它只是寻找到 i2c_adapter 对应的 i2c_algorithm,并使用 i2c_algorithm 的master_xfer()

int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)
{

    int ret;

    if (adap->algo->master_xfer) {

        down(&adap->bus_lock);

        ***ret = adap->algo->master_xfer(adap,msgs,num); /* 消息传输 */***

        up(&adap->bus_lock);

        return ret;

    } else {

        dev_dbg(&adap->dev, "I2C level transfers not supported\n");

        return -ENOSYS;

    }

}