[Android]Linux kernel 開發基礎 （四）- 新增I2C device 範例

新增platform device 範例 是直接向platform bus註冊一個裝置
其他較常見的裝置要註冊也是大同小異,
makefile 與 kconfig 寫法是相同的,差異在於在哪個Bus下註冊裝置
底下為新增I2C device 範例：
1. makefile
根據kconfig的設定,定義要build的檔案
例如範例中的
obj-$(CONFIG_HELLO_DRIVER) += hello.o
這裡定義了：當CONFIG_HELLO_DRIVER為y
就將hello這個檔案build進kernel

2. kconfig
定義了driver 簡易描述以及預設值,與makefile一起,為kernel建立tree管理之用,
在make menuconfig時,可將該driver相關訊息顯示在視窗界面
config HELLO_DRIVER
    default y
    tristate "Hello Driver"
help
  Say Y here if you want to enable hello driver.
這裡定義了一個新的driver HELLO_DRIVER,,
預設值為y

3.如果要向I2C bus註冊新裝置,必須先找到I2C bus initial 的檔案（根據每個BSP設計不同,這個位置與名稱也不同,通常位於kernel/arch/arm/"cpu_name"）,透過i2c_register_board_info來註冊新裝置,
(參考自: https://www.kernel.org/doc/htmldocs/device-drivers/API-i2c-register-board-info.html)

Name

i2c_register_board_info — statically declare I2C devices

Synopsis

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

Arguments

busnum

identifies the bus to which these devices belong

info

vector of i2c device descriptors

len

how many descriptors in the vector; may be zero to reserve the specified bus number.

例如:
i2c_register_board_info(i2c_bus_num, i2c_devs_define, ARRAY_SIZE(i2c_devs_define));

而i2c_devs_define 必須明確指出i2c device address 與i2c_bus_num才能根據設定將資料送到該裝置 ,定義範例如下:

static struct i2c_board_info i2c_devs_define[] __initdata = {
{
I2C_BOARD_INFO(i2c_device_name, i2c_address >> 1),
.irq = IRQ_EINT(IRQ_num),
},
};

4.最後調用i2c_add_driver（&i2c_driver）;即可完成I2C device 新增

static const unsigned short normal_i2c[2] = {i2c_address,I2C_CLIENT_END};
static struct i2c_driver i2c_driver = {
.driver = {
.name = i2c_device_name,
.owner = THIS_MODULE,
},
.class = I2C_CLASS_HWMON,
.address_list = normal_i2c,
.id_table = id,
.probe = probe,
.remove = __exit_p(remove),
.suspend = suspend,
    .resume = resume,

};
i2c_add_driver(&i2c_driver);