Linux内核---32.I2C设备驱动分析

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一. I2C设备的定义及其添加过程
1.1 数据结构
include/linux/i2c.h:

struct i2c_board_info {
    char        type[I2C_NAME_SIZE];            //设备名   
    unsigned short    flags;                    //   
    unsigned short    addr;                     //     
    void        *platform_data;                 // 
    struct dev_archdata    *archdata;           // 
    struct device_node *of_node;                // 
    int        irq;                             // 
};

drivers/i2c/i2c-core.h:

struct i2c_devinfo {
    struct list_head    list;                 //i2c设备列表头           
    int            busnum;                    //i2c总线并不是只有一条
    struct i2c_board_info    board_info;      //
};

1.2 全局变量
drivers/i2c/i2c-core.h:

extern struct rw_semaphore    __i2c_board_lock;      //    
extern struct list_head    __i2c_board_list;         // 
extern int        __i2c_first_dynamic_bus_num;       //

全局变量的初始化,在driver/i2c/i2c-boardinfo.c中

DECLARE_RWSEM(__i2c_board_lock);                     //读写锁
EXPORT_SYMBOL_GPL(__i2c_board_lock);

LIST_HEAD(__i2c_board_list);                         //双向链表
EXPORT_SYMBOL_GPL(__i2c_board_list);

int __i2c_first_dynamic_bus_num;
EXPORT_SYMBOL_GPL(__i2c_first_dynamic_bus_num);

1.3 I2C设备的定义
在arch/arm/mach-s3c64xx/mach-smdk6410.c中,定义了I2C的设备

static struct i2c_board_info i2c_devs0[] __initdata = {
    { I2C_BOARD_INFO("ov965x", 0x30), }, // gjl
};

static struct i2c_board_info i2c_devs1[] __initdata = {
    { I2C_BOARD_INFO("24c128", 0x57), },    /* Samsung S524AD0XD1 */
};

其中 #define I2C_BOARD_INFO(dev_type, dev_addr) \
.type = dev_type, .addr = (dev_addr)
.type 是name
.addr 是设备在i2c上的地址

在arch/arm/mach-s3c64xx/mach-smdk6410.c中

static void __init smdk6410_machine_init(void)
{
    i2c_register_board_info(0, i2c_devs0, ARRAY_SIZE(i2c_devs0));   //将bus 0上的设备添加到i2c的设备链表中
    i2c_register_board_info(1, i2c_devs1, ARRAY_SIZE(i2c_devs1));   //将bus 1上的设备添加到i2c的设备链表中
}

在driver/i2c/i2c-boardinfo.c中:

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

    down_write(&__i2c_board_lock);
    
    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);    
        
        devinfo->busnum = busnum;                           //新建一个i2c_devinfo结构体,初始化之后
        devinfo->board_info = *info;                        //初始化后,插入到i2c设备链表的尾部
        list_add_tail(&devinfo->list, &__i2c_board_list);   //在全局变量i2c_board_list中添加新的设备
    }

    up_write(&__i2c_board_lock);

    return status;
}

1.4 I2C设备的添加过程
s3c24xx_i2c_probe
    --> i2c_add_numbered_adapter
        --> i2c_register_adapter
            --> i2c_scan_static_board_info
                --> i2c_new_device
i2c设备的添加过程是随着i2c控制器的添加而添加的,这个在下一篇中详细说一下,这儿就省了!

二. I2C设备驱动的注册过程
这儿以ov9650为例说明一下,(为什么呢? 因为ok6410上面没有其它的i2c设备了!)
drivers/media/video/samsung/fimc/ov965x.c

static __init int ov965x_init(void)
{
    return i2c_add_driver(&ov965x_i2c_driver);
}
module_init(ov965x_init)

ov965x_init
--> i2c_add_driver

static inline int i2c_add_driver(struct i2c_driver *driver)
{
    return i2c_register_driver(THIS_MODULE, driver);
}

在driver/i2c/i2c-core.c中
int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
    driver->driver.owner = owner;
    driver->driver.bus = &i2c_bus_type;
    res = driver_register(&driver->driver);        //注册driver并进入I2C的probe函数
    INIT_LIST_HEAD(&driver->clients);
                                                    //对i2c上的每一个设备执行一次__process_new_driver                 
    i2c_for_each_dev(driver, __process_new_driver); //但__process_new_driver好像什么事也没有干
    return 0; 
}
EXPORT_SYMBOL(i2c_register_driver);

ov965x_init
--> i2c_add_driver
--> i2c_device_probe
driver/i2c/i2c-core.c

static int i2c_device_probe(struct device *dev)
{
    struct i2c_client    *client = i2c_verify_client(dev);   //这儿己经是ov965x的dev了,己经得到dev->addr=0x30
    struct i2c_driver    *driver;
    int status;

    driver = to_i2c_driver(dev->driver);
    client->driver = driver;
    if (!device_can_wakeup(&client->dev))
        device_init_wakeup(&client->dev, client->flags & I2C_CLIENT_WAKE);
    status = driver->probe(client, i2c_match_id(driver->id_table, client));    //开始调用具体设备的probe
    return status;
}

下面接着分析

三. I2C设备驱动的写过程
i2c_device_probe
--> ov965x_probe

static int ov965x_probe(struct i2c_client *c, const struct i2c_device_id *id)
{
    ov965x_data.client = c;
    s3c_fimc_register_camera(&ov965x_data);            //向fimc注册
    for (i = 0; i < OV965X_INIT_REGS; i++) {           //通过i2c写ov9650的寄存器
        ret = i2c_smbus_write_byte_data(c, OV965X_init_reg[i].subaddr, OV965X_init_reg[i].value);
    }
    return 0;
}

i2c_device_probe
--> ov965x_probe
--> i2c_smbus_write_byte_data
driver/i2c/i2c-core.c

s32 i2c_smbus_write_byte_data(const struct i2c_client *client, u8 command, u8 value)
{
    union i2c_smbus_data data;
    data.byte = value;
    return i2c_smbus_xfer(client->adapter, client->addr, client->flags,
             I2C_SMBUS_WRITE, command, I2C_SMBUS_BYTE_DATA, &data);
}

s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
         char read_write, u8 command, int protocol,
         union i2c_smbus_data *data)
{
    flags &= I2C_M_TEN | I2C_CLIENT_PEC;    
    i2c_smbus_xfer_emulated(adapter, addr, flags, read_write, command, protocol, data);
}

i2c_device_probe
    --> ov965x_probe
        --> i2c_smbus_write_byte_data
            -->  i2c_smbus_xfer_emulated
driver/i2c/i2c-core.c

static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
             unsigned short flags,
             char read_write, u8 command, int size,
             union i2c_smbus_data *data)
{
    unsigned char msgbuf0[I2C_SMBUS_BLOCK_MAX+3];
    unsigned char msgbuf1[I2C_SMBUS_BLOCK_MAX+2];
    int num = read_write == I2C_SMBUS_READ ? 2 : 1;
    struct i2c_msg msg[2] = { { addr, flags, 1, msgbuf0 },
     { addr, flags | I2C_M_RD, 0, msgbuf1 }
     };

    msgbuf0[0] = command;
    switch (size) {
    case I2C_SMBUS_BYTE_DATA:       
            msg[0].len = 2;
            msgbuf0[1] = data->byte;        
        break;
    }

    status = i2c_transfer(adapter, msg, num);    //把要传输的信息组装成msg,进行传输
    //i==0 && I2C_SMBUS_READ
}

i2c_device_probe
    --> ov965x_probe
        --> i2c_smbus_write_byte_data
            -->  i2c_smbus_xfer_emulated
                --> i2c_transfer
driver/i2c/i2c-core.c

int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
    unsigned long orig_jiffies;
    int ret, try;
    if (in_atomic() || irqs_disabled()) {
        ret = i2c_trylock_adapter(adap);
        if (!ret)
            return -EAGAIN;
    } else 
        i2c_lock_adapter(adap);       //加把锁
        
    orig_jiffies = jiffies;
    for (ret = 0, try = 0; try <= adap->retries; try++) {          //如果传输失败,则重试adap->retries次
        ret = adap->algo->master_xfer(adap, msgs, num);            //传输函数,在文件i2c-s3c2410.c中
        if (ret != -EAGAIN)
            break;
        if (time_after(jiffies, orig_jiffies + adap->timeout))    //如果超时了,不管成不成功立即返回
            break;
    }
    i2c_unlock_adapter(adap);        //unlock
    return ret; 
}

注: ret = adap->algo->master_xfer(adap, msgs, num); 是i2c控制器的数据传输函数,下一篇分析

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