前言
首先:设备树上只要拥有compatible属性的节点,都会自己被添加到platform总线上,保存在device链表中。i2c控制器也是在这个时候被添加的,主板上有几个i2c接口就有几个i2c控制器(adapter)
其次:因为控制器device被添加到了platform总线上,所以控制器驱动也需要被注册到platform总线上,使之能匹配到device,驱动很重要的一点就是向i2c总线注册adapter(控制器),调用i2c_add_numbered_adapter接口
i2c总线的初始化
postcore_initcall(i2c_init);
在i2c_init里面进行总线的注册的 ,所以i2c驱动注册不应该早于postcore_initcall```
## 1.i2c_add_numbered_adapter
```c
int i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
//由系统自动加载的platform_device的id都为-1,所以一般取device->id值的这里也为-1
if (adap->nr == -1) /* -1 means dynamically assign bus id */
return i2c_add_adapter(adap);
return __i2c_add_numbered_adapter(adap);
}
i2c_add_adapter
->i2c_register_adapter
static int i2c_register_adapter(struct i2c_adapter *adap)
{
...
dev_set_name(&adap->dev, "i2c-%d", adap->nr);
//BUS指向I2C
adap->dev.bus = &i2c_bus_type;
adap->dev.type = &i2c_adapter_type;
//这里就是把device添加到Bus的device链表尾部,这个函数我在platform设备加载里面有详细分析,这里不在介绍
res = device_register(&adap->dev);
...
adapter设备是I2c总线上最早添加上去的device.
由于所有的i2c device都挂在i2c控制器下,所以添加完成adapter就向主动去加载这个adapter节点下的所有子节点,并添加到i2c总线设备链表上去
i2c_add_adapter
->i2c_register_adapter
->of_i2c_register_devices
->of_i2c_register_device
代码如下:
int of_modalias_node(struct device_node *node, char *modalias, int len)
{
const char *compatible, *p;
int cplen;
compatible = of_get_property(node, "compatible", &cplen);
if (!compatible || strlen(compatible) > cplen)
return -ENODEV;
p = strchr(compatible, ',');
strlcpy(modalias, p ? p + 1 : compatible, len);
return 0;
}
static struct i2c_client *of_i2c_register_device(struct i2c_adapter *adap,
struct device_node *node)
{
struct i2c_client *result;
struct i2c_board_info info = {
};
struct dev_archdata dev_ad = {
};
const __be32 *addr_be;
u32 addr;
int len;
dev_dbg(&adap->dev, "of_i2c: register %s\n", node->full_name);
if (of_modalias_node(node, info.type, sizeof(info.type)) < 0) {
dev_err(&adap->dev, "of_i2c: modalias failure on %s\n",
node->full_name);
return ERR_PTR(-EINVAL);
}
addr_be = of_get_property(node,