/**
* i2c_master_send - issue a single I2C message in master transmit mode
* @client: Handle to slave device
* @buf: Data that will be written to the slave
* @count: How many bytes to write, must be less than 64k since msg.len is u16
*
* Returns negative errno, or else the number of bytes written.
*/
int i2c_master_send(struct i2c_client *client, const char *buf, int count)
{
        int ret;
        struct i2c_adapter *adap = client->adapter;
        struct i2c_msg msg;

        msg.addr = client->addr;
        msg.flags = client->flags & I2C_M_TEN;
        msg.len = count;
        msg.buf = (char *)buf;

        ret = i2c_transfer(adap, &msg, 1);

        /* If everything went ok (i.e. 1 msg transmitted), return #bytes
           transmitted, else error code. */
        return (ret == 1) ? count : ret;
}
EXPORT_SYMBOL(i2c_master_send);

/**
* i2c_master_recv - issue a single I2C message in master receive mode
* @client: Handle to slave device
* @buf: Where to store data read from slave
* @count: How many bytes to read, must be less than 64k since msg.len is u16
*
* Returns negative errno, or else the number of bytes read.
*/
int i2c_master_recv(struct i2c_client *client, char *buf, int count)
{
        struct i2c_adapter *adap = client->adapter;
        struct i2c_msg msg;
        int ret;

        msg.addr = client->addr;
        msg.flags = client->flags & I2C_M_TEN;
        msg.flags |= I2C_M_RD;
        msg.len = count;
        msg.buf = buf;

        ret = i2c_transfer(adap, &msg, 1);

        /* If everything went ok (i.e. 1 msg transmitted), return #bytes
           transmitted, else error code. */
        return (ret == 1) ? count : ret;
}
EXPORT_SYMBOL(i2c_master_recv);

static s32 ov5640_write_reg(u16 reg, u8 val)
{
        u8 au8Buf[3] = {0};

        au8Buf[0] = reg >> 8;
        au8Buf[1] = reg & 0xff;
        au8Buf[2] = val;

        if (i2c_master_send(ov5640_data.i2c_client, au8Buf, 3) < 0) {
                pr_err("%s:write reg error:reg=%x,val=%x\n",
                        __func__, reg, val);
                return -1;
        }

        return 0;
}

static s32 ov5640_read_reg(u16 reg, u8 *val)
{
        u8 au8RegBuf[2] = {0};
        u8 u8RdVal = 0;

        au8RegBuf[0] = reg >> 8;
        au8RegBuf[1] = reg & 0xff;

        if (2 != i2c_master_send(ov5640_data.i2c_client, au8RegBuf, 2)) {
                pr_err("%s:write reg error:reg=%x\n",
                                __func__, reg);
                return -1;
        }
        if (1 != i2c_master_recv(ov5640_data.i2c_client, &u8RdVal, 1)) {
                pr_err("%s:read reg error:reg=%x,val=%x\n",
                                __func__, reg, u8RdVal);
                return -1;
        }

        *val = u8RdVal;

        return u8RdVal;
}

help

i2c help

root@arm9260:~# i2cdetect -y 0
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
70: 70 -- -- -- -- -- -- --