关于i2c_register_board_info()函数

i2c_register_board_info()函数用于往__i2c_board_list这条链表添加一条i2c设备信息，在i2c adapter注册的时候，会扫描__i2c_board_list链表，然后调用i2c_new_device()函数来注册i2c设备，注意，要先于i2c adapter注册之前就添加好i2c设备信息，否则会出现调用了i2c_register_board_info()函数，而设备不能注册的情况。

i2c_register_board_info()函数如下：

int __init
i2c_register_board_info(int busnum,
struct i2c_board_info const *info, unsigned len)
{
int status;

down_write(&__i2c_board_lock);

/* dynamic bus numbers will be assigned after the last static one */
if (busnum >= __i2c_first_dynamic_bus_num)
__i2c_first_dynamic_bus_num = busnum + 1;

for (status = 0; len; len--, info++) {
struct i2c_devinfo	*devinfo;

devinfo = kzalloc(sizeof(*devinfo), GFP_KERNEL);
if (!devinfo) {
pr_debug("i2c-core: can't register boardinfo!\n");
status = -ENOMEM;
break;
}

devinfo->busnum = busnum;
devinfo->board_info = *info;
list_add_tail(&devinfo->list, &__i2c_board_list);
}

up_write(&__i2c_board_lock);

return status;
}

注册i2c总线流程如下：

i2c_add_numbered_adapter()->i2c_register_adapter()

在i2c_register_adapter()函数中调用了i2c_scan_static_board_info()函数，代码如下：

static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
{
struct i2c_devinfo	*devinfo;

down_read(&__i2c_board_lock);
list_for_each_entry(devinfo, &__i2c_board_list, list) {
if (devinfo->busnum == adapter->nr
&& !i2c_new_device(adapter,
&devinfo->board_info))
dev_err(&adapter->dev,
"Can't create device at 0x%02x\n",
devinfo->board_info.addr);
}
up_read(&__i2c_board_lock);
}

i2c_scan_static_board_info()函数先扫描__i2c_board_list，然后调用i2c_new_device()函数来注册i2c设备。这就是静态注册i2c设备的方法，一般在板级的初始化函数中调用i2c_register_board_info()函数来完成i2c设备信息的添加。

除了这种方法外，Linux还提供了另外的方法来注册i2c设备。例如：static const unsigned short normal_i2c[] = { 0x2c, 0x2d, I2C_CLIENT_END };

static int __devinit usb_hcd_pnx4008_probe(struct platform_device *pdev)
{
(...)
struct i2c_adapter *i2c_adap;
struct i2c_board_info i2c_info;

(...)
i2c_adap = i2c_get_adapter(2);
memset(&i2c_info, 0, sizeof(struct i2c_board_info));
strlcpy(i2c_info.name, "isp1301_pnx", I2C_NAME_SIZE);
isp1301_i2c_client = i2c_new_probed_device(i2c_adap, &i2c_info,
normal_i2c);
i2c_put_adapter(i2c_adap);
(...)
}来自Documentation/i2c/instantiating-devices。