節點創建

i2c_add_adapter、i2c_add_numbered_adapter 是注冊 i2c_adapter，這兩個 API 最終是調用 i2c_register_adapter。

static int i2c_register_adapter(struct i2c_adapter *adap)
{
 ......

 dev_set_name(&adap- >dev, "i2c-%d", adap- >nr);
 adap- >dev.bus = &i2c_bus_type;
 adap- >dev.type = &i2c_adapter_type;
 res = device_register(&adap- >dev);

 /* create pre-declared device nodes */
 of_i2c_register_devices(adap);
 i2c_acpi_install_space_handler(adap);
 i2c_acpi_register_devices(adap);

  .....
}

dev_set_name(&adap->dev, "i2c-%d", adap->nr) 會在 Linux 中自動創建 /sys/devices/platform/11f00000.i2c6/i2c-6 節點。

of_i2c_register_devices 會調用 i2c_new_client_device

struct i2c_client *i2c_new_client_device(struct i2c_adapter *adap, struct i2c_board_info const *info)
{
  ......

 client- >dev.parent = &client- >adapter- >dev;
 client- >dev.bus = &i2c_bus_type;
 client- >dev.type = &i2c_client_type;
 client- >dev.of_node = of_node_get(info- >of_node);
 client- >dev.fwnode = info- >fwnode;

 device_enable_async_suspend(&client- >dev);
 i2c_dev_set_name(adap, client, info);

  ......

 status = device_register(&client- >dev);

  ......
}

i2c_dev_set_name 會在 Linux 系統中自動創建 /sys/devices/platform/11f00000.i2c6/i2c-6/6-0058 ，這里是掛在某個 i2c bus 上的，從機地址為 0x58 的設備節點。

到這里，大家應該能看懂下圖，這些節點在 I2C 控制器驅動加載時，自動創建的。大家在 I2C 控制器的子節點中聲明的 I2C 從機設備，也會在這一步創建節點。