IIC bus realizes client device

One 、Linux I2C Introduction to drive frame

I2C Bus and platform Bus is similar , It's just platform Bus is a virtual bus , and I2C The bus actually exists .

Linux Medium l2C It is also designed according to the platform bus model , Since it is also designed according to the platform bus model , Is it also divided into one device And a driver Well ？ however I2C there device Don't cry device, But is called client.
 

among I2C Bus driver is SOC Of I2C Controller drive , Generally speaking, it is SOC The manufacturer has achieved good . and I2C The device driver is the user according to their own different devices actualized . The drive of each device is different , But the writing process is one . Let's analyze it in detail .

Two 、 Device side code writing

1、 Do not use device tree files

When you start writing I2C When the device is driven , First, add device information . First, let's take a look at not using the device tree , When using platform files , How to add I2C Equipment information . Pass in the platform file i2c_board_info Structure to describe a specific I2C equipment .

struct i2c_board_info 
{  
    char type[I2C_NAME_SIZE]; /* I2C  Device name  */ 
    unsigned short flags; /*  sign  */ 
    unsigned short addr; /* I2C  Device address  */ 
    void *platform_data; 
    struct dev_archdata *archdata; 
    struct device_node *of_node;
    struct fwnode_handle *fwnode; 
    int irq; 
};

In practical use , Usually use I2C_BOARD_INFO Honglai Set up i2c_board_info Of type and addr These two member variables . for example ：

static struct i2c_board_info mx27_3ds_i2c_camera = 
{ 
    I2C_BOARD_INFO("ov2640", 0x30), 
};

Example ：

#include <linux/init.h> 
#include <linux/module.h> 
#include <linux/i2c.h>

struct i2c adapter*i2c_ada;

// Allocate one I2C_client The pointer 
struct i2c_cllent*i2c_client;

// Supported by I2C Device list for 
struct i2c board_info ft5x06_info[]=
{
    // Each item represents a I2C equipment , This sentence means that the name of this device is ft5×06_test, The device address is 0×38
    {I2C_BOARD_INFO("ft5×06_test",0x38)},
}

static int ft5x06_client_init(void）
{
    // call i2c_get_adapter To obtain a I2C Bus . because t5x06 It is attached to I2C2 On ,
    // So this parameter is 1, from 0 Numbered starting 
    i2c_ada=i2c_get_adapter(1);

    // hold I2C CLIENT and I2C Devices are associated 
    i2c_client=i2c_new_device(i2c_ada,ft5x06_info);

    i2c_put_adapter(i2c_ada);// Release I2q 

    return e;
}

static void ft5x06_client_exit(void)
{
    i2c_unregister_device(i2c_client);
}

module_init(ft5x06_client_init); 
module_exit(ft5x06_client_exit); 
MODULE_LICENSE("GPL"); 

2、 Use the device tree file

When using device tree files , Just add the corresponding... In the device tree file I2C The device node is ok

After loading the device tree , stay sys/bus/i2c/devices You can see it under the directory iic Equipment

In the device tree reg It's settings IIC The address of the device  , therefore ,edt-ft5x06 The device address of is 0x38

3、 ... and 、driver Side code writing

The basic flow ：

• i2c_driver Structure initialization
• After the initialization is completed, the i2c_driver Register into the kernel ,i2c_add_driver
• When the device and driver match successfully , Will execute probe function ,probe Function is to execute a set of processes driven by character devices .

#include <linux/init.h> 
#include <linux/module.h> 
#include <linux/i2c.h>

static const struct i2c_device_id ft5x06_id_ts[]={
    {"xxx",0},
    {}
};

static const struct of_device_id ft5x06_id[]=
{
    {.compatible="edt,edt-ft5306",0,},
    {.compatible="edt,edt-ft5x06",0,},
    {.compatible="edt,edt-ft5406",0,},
    {}
}; 

static struct i2c_driver ft5x06_driver={
    .driver={
        .owner=THIS_MODULE,
        .name="ft5×06 test",
        .of_match_table=ft5×06_id,// and device Match to use 
    },
    .probe=ft5x06_probe,
    .remove=ft5x06_remove,
    .idtable=ft5x06_id_ts// It is also used for matching , Usually use of_match_table.
};

int(*probe)(struct l2c_client *i2c_cllent, const struct 12c_device_id * id)
{    
    // You can register one here misc Equipment or char Equipment 
}



static int ft5x06_driver_init(void）
{
    int ret; 
    ret=i2c_add_driver(&ft5x06_driver); 
    if(ret<0){
        printk("i2c_add_ driver is error\n"); 
        return ret;
    }
}

static void ft5x06_driver_exit(void)
{
    i2c_del_driver(&ft5xo6_driver);
}

module_init(ft5x06_driver_init); 
module_exit(ft5x06_driver_exit); 
MODULE_LICENSE("GPL");