[聚合文章] Android/Linux I2C 驱动架构分析

# alps\kernel-3.18\drivers\i2c

# alps\kernel-3.18\include\linux\i2c.h

/*
 * 表示一个 i2c 适配器，即挂接在 i2c 总线上的 i2c 控制器
 * i2c_adapter is the structure used to identify a physical i2c bus along
 * with the access algorithms necessary to access it.
 */
struct i2c_adapter {
	struct module *owner;
	unsigned int class;		  /* classes to allow probing for */
	const struct i2c_algorithm *algo; /* the algorithm to access the bus */
	struct device dev;		/* the adapter device */
	....

};

/*
 * 表示一个 i2c 设备驱动
 */
struct i2c_driver {
	unsigned int class;

	/* Standard driver model interfaces */
	int (*probe)(struct i2c_client *, const struct i2c_device_id *); // 匹配 i2c 设备（i2c_client）
	int (*remove)(struct i2c_client *);
    ...

	struct device_driver driver;   
	const struct i2c_device_id *id_table; // 此设备驱动服务的设备 ID

	int (*detect)(struct i2c_client *, struct i2c_board_info *);
	const unsigned short *address_list; // 此设备驱动支持的设备地址
	struct list_head clients;  // 挂接此设备驱动匹配成功 i2c_client
};

/*
 * 表示一个 i2c 设备
 */
struct i2c_client {
	unsigned short flags;		/* div., see below		*/
	unsigned short addr;		/* chip address - NOTE: 7bit	*/
					/* addresses are stored in the	*/
					/* _LOWER_ 7 bits		*/
	char name[I2C_NAME_SIZE];
	struct i2c_adapter *adapter;	/* the adapter we sit on	*/
	struct device dev;		/* the device structure		*/
	int irq;			/* irq issued by device		*/
	struct list_head detected;
#ifdef CONFIG_MTK_I2C_EXTENSION
	__u32 timing;			/* parameters of timings		*/
	__u32 ext_flag;
#endif
};

/*
 * 描述 i2c 设备信息
 */
struct i2c_board_info {
	char		type[I2C_NAME_SIZE];
	unsigned short	flags;
	unsigned short	addr;
	void		*platform_data;
	struct dev_archdata	*archdata;
	struct device_node *of_node;
	struct acpi_dev_node acpi_node;
	int		irq;
};


# alps\kernel-3.18\include\uapi\linux\i2c.h
/*
 * 表示一个 i2c 数据包
 */
struct i2c_msg {
	__u16 addr;	     /* slave address */
	__u16 flags;
#define I2C_M_TEN		0x0010	/* this is a ten bit chip address */
...
#define I2C_M_RECV_LEN		0x0400	/* length will be first received byte */
	__u16 len;		/* msg length				*/
	__u8 *buf;		/* pointer to msg data			*/
#ifdef CONFIG_MTK_I2C_EXTENSION
	__u32 timing;	/* parameters of timings		*/
	__u32 ext_flag;
#endif
};

# alps\kernel-3.18\arch\arm64\boot\dts\mt6797.dtsi
# alps\kernel-3.18\arch\arm64\boot\dts\aeon6797_6m_n.dts


# alps\kernel-3.18\drivers\i2c
i2c-core.c：i2c核心层，设备驱动和总线驱动的桥梁
i2c-dev.c：通用 i2c 设备驱动
busses：开源的 adapter 
algos：i2c 通信算法

# alps\kernel-3.18\include\linux\i2c.h
# alps\kernel-3.18\include\uapi\linux\i2c.h

# alps\kernel-3.18\drivers\i2c\i2c-dev.c （也可以是其他设备驱动文件，如：ov9650.c等。）
static const struct file_operations i2cdev_fops = {
	.owner		= THIS_MODULE,
	.llseek		= no_llseek,
	.read		= i2cdev_read,
	.write		= i2cdev_write,
	.unlocked_ioctl	= i2cdev_ioctl,
	.open		= i2cdev_open,
	.release	= i2cdev_release,
};


i2cdev_read()
    i2c_master_recv()
    copy_to_user()
i2cdev_write()
    memdup_user()  // 分配内核空间，用户态到内核态的拷贝
        copy_from_user()
    i2c_master_send()
...
i2cdev_open()
    i2c_dev_get_by_minor()
    i2c_get_adapter()
    // 设置 i2c client

i2c_dev_init()
    register_chrdev(I2C_MAJOR, "i2c", &i2cdev_fops)
    i2cdev_attach_adapter() // 绑定存在的 i2c 控制器（adapter）
        adap = to_i2c_adapter(dev);
	    i2c_dev = get_free_i2c_dev(adap);
	    /* register this i2c device with the driver core */
	    i2c_dev->dev = device_create(..."i2c-%d")

# jni
extern "C" {
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_open()
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_read()
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_write()
...
}

# app
I2c.open(“/dev/i2c-x”)
...

public static class I2c {  
        ...
        public native int open(); 
        public native int read(); 
        public native int write();  
        ...
}