Linux I2C core
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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; }}
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