上一篇文章我们介绍了使用devfs访问IIC设备，下面再来介绍应用sysfs方法访问IIC。

 

在这里，系统要用到三个很重要的结构——i2c_client、i2c_driver和i2c_adapter。i2c_client指的是IIC设备，我的开发板上的IIC设备就是AT24C02的eeprom；i2c_driver指的是IIC的设备驱动；i2c_adapter指的是IIC的适配器，也就是2440集成的IIC总线。要形成IIC的sysfs文件系统，就必须创建这三个结构，并把它们关联起来。

 

一、i2c_client、i2c_driver和i2c_adapter结构的创建

 

我们先来看看这三个结构是如何被定义的。

 

在mach-zhaocj2440.c文件中的zhaocj2440_init函数内，有下面一句：

i2c_register_board_info(0,zhaocj2440_i2c_devs,ARRAY_SIZE(zhaocj2440_i2c_devs));

 

i2c_register_board_info函数是在drivers/i2c/i2c-boardinfo.c中被定义，作用是静态注册声明开发板上的IIC信息。其中该函数的参数zhaocj2440_i2c_devs的作用是定义板上的IIC设备信息，它是在mach-zhaocj2440.c内定义的。由于我的开发板上的IIC设备为AT24C02的eeprom，因此zhaocj2440_i2c_devs应该重新定义为：

static struct i2c_board_info zhaocj2440_i2c_devs[] __initdata = {

       {

              I2C_BOARD_INFO("24c02", 0x50),   //宏定义：.type=24c02, .addr=0x50,

              .platform_data= &at24c02,

       },

};

 

而at24c02定义为：

static struct at24_platform_data at24c02 = {

       .byte_len = SZ_2K / 8,                //容量大小

       .page_size       = 8,                      //每页的字节数

};

 

i2c_board_info.type就是i2c_client.name变量，i2c_board_info.addr就是i2c_client.addr变量，所以只要定义了zhaocj2440_i2c_devs，也就是定义了i2c_client结构。关于这一点，我们在后面会讲到。

 

我们再来看drivers/misc/eeprom/at24.c文件中的模块初始化函数at24_init：

static int __init at24_init(void)

{

       if(!io_limit) {

              pr_err("at24:io_limit must not be 0!\n");

              return -EINVAL;

       }

 

       io_limit= rounddown_pow_of_two(io_limit);

       //为IIC添加驱动

       return i2c_add_driver(&at24_driver);

}

 

i2c_add_driver函数通过宏定义为i2c_register_driver函数，它的作用是注册IIC驱动，这里的驱动是at24_driver，它的定义为：

static struct i2c_driver at24_driver = {

       .driver= {

              .name= "at24",

              .owner= THIS_MODULE,

       },

       .probe= at24_probe,

       .remove= __devexit_p(at24_remove),

       .id_table= at24_ids,

};

 

IIC适配器是通过i2c-s3c2410.c文件内的s3c24xx_i2c_probe函数创建的。该函数调用了i2c_add_numbered_adapter函数，它又调用了i2c_register_adapter函数，从而完成了对i2c_adapter的创建和注册。

 

二、i2c_client、i2c_driver和i2c_adapter三者的绑定

 

这样，i2c_client、i2c_driver和i2c_adapter都被创建了，并都各自放到了总线上，那它们是如何关联在一起的呢？

 

在s3c24xx_i2c_probe函数内调用了of_i2c_register_devices函数，该函数提取出了i2c_board_info设备信息，并且又调用了i2c_new_device函数，该函数主要完成了两项工作，一是通过把i2c_board_info赋值给i2c_client，从而创建了i2c_client，因此正如我们在前面介绍过的，定义了i2c_board_info，也就是定义了i2c_client；二是把刚刚创建的IIC设备与在s3c24xx_i2c_probe函数创建的IIC适配器绑定在了一起，如下面这句：

client->adapter= adap;

 

如前文所述，i2c_register_adapter函数用于注册i2c_adapter，i2c_register_driver函数用于注册i2c_driver。i2c_register_adapter函数有下面一句：

adap->dev.bus= &i2c_bus_type;

i2c_register_driver函数有下面一句：

driver->driver.bus= &i2c_bus_type;

 

总之，都定义了IIC的总线类型——i2c_bus_type：

struct bus_type i2c_bus_type = {

       .name             ="i2c",

       .match            =i2c_device_match,

       .probe            =i2c_device_probe,

       .remove          =i2c_device_remove,

       .shutdown       = i2c_device_shutdown,

       .pm         = &i2c_device_pm_ops,

};

 

当设备或驱动添加到总线上时，会调用match指向的函数，用于找到是否有设备和驱动相匹配；当设备或驱动添加到总线上时，也会调用probe指向的函数，用于初始化与驱动相匹配的设备。因此无论是在创建i2c_adapter，还是i2c_driver的时候，都会调用这两个函数。

static int i2c_device_match(struct device *dev, structdevice_driver *drv)

{

       structi2c_client      *client = i2c_verify_client(dev);

       structi2c_driver     *driver;

 

       if(!client)

              return0;

 

       /*Attempt an OF style match */

       //设备和驱动是否匹配

       if(of_driver_match_device(dev, drv))

              return1;

 

       driver= to_i2c_driver(drv);

       /*match on an id table if there is one */

       //如果驱动有设备列表，则用下面判断设备和驱动是否匹配

       if(driver->id_table)

              returni2c_match_id(driver->id_table,client) != NULL;

 

       return0;

}

 

i2c_device_match函数返回非零值，表示设备和驱动匹配上了。at24_driver中有一个设备列表项——at24_ids：

static const struct i2c_device_id at24_ids[] = {

       /*needs 8 addresses as A0-A2 are ignored */

       {"24c00",AT24_DEVICE_MAGIC(128 / 8, AT24_FLAG_TAKE8ADDR) },

       /*old variants can't be handled with this generic entry! */

       {"24c01",AT24_DEVICE_MAGIC(1024 / 8, 0) },

       {"24c02",AT24_DEVICE_MAGIC(2048 / 8, 0) },

       /*spd is a 24c02 in memory DIMMs */

       {"spd", AT24_DEVICE_MAGIC(2048 / 8,

              AT24_FLAG_READONLY| AT24_FLAG_IRUGO) },

       {"24c04",AT24_DEVICE_MAGIC(4096 / 8, 0) },

       /*24rf08 quirk is handled at i2c-core*/

       {"24c08",AT24_DEVICE_MAGIC(8192 / 8, 0) },

       {"24c16",AT24_DEVICE_MAGIC(16384 / 8, 0) },

       {"24c32",AT24_DEVICE_MAGIC(32768 / 8, AT24_FLAG_ADDR16) },

       {"24c64",AT24_DEVICE_MAGIC(65536 / 8, AT24_FLAG_ADDR16) },

       {"24c128",AT24_DEVICE_MAGIC(131072 / 8, AT24_FLAG_ADDR16) },

       {"24c256",AT24_DEVICE_MAGIC(262144 / 8, AT24_FLAG_ADDR16) },

       {"24c512",AT24_DEVICE_MAGIC(524288 / 8, AT24_FLAG_ADDR16) },

       {"24c1024",AT24_DEVICE_MAGIC(1048576 / 8, AT24_FLAG_ADDR16) },

       {"at24", 0 },

       {/* END OF LIST */ }

};

 

上面结构中的一项"24c02"，与我们前面定义的i2c_client.name一致，因此i2c_client和i2c_driver匹配上了。

 

static int i2c_device_probe(struct device *dev)

{

       structi2c_client      *client = i2c_verify_client(dev);

       structi2c_driver     *driver;

       intstatus;

 

       if(!client)

              return0;

 

       //提取IIC驱动

       driver = to_i2c_driver(dev->driver);

       if(!driver->probe || !driver->id_table)

              return-ENODEV;

       //i2c_client和i2c_driver绑定在了一起

       client->driver= driver;

       if(!device_can_wakeup(&client->dev))

              device_init_wakeup(&client->dev,

                                   client->flags& I2C_CLIENT_WAKE);

       dev_dbg(dev,"probe\n");

 

       //调用probe函数，也就是at24_probe函数

       status= driver->probe(client, i2c_match_id(driver->id_table,client));

       if(status) {

              client->driver= NULL;

              i2c_set_clientdata(client, NULL);

       }

       returnstatus;

}

 

经过上面的分析，可以看出IIC设备中的驱动指向了IIC驱动，IIC设备中的适配器指向了IIC适配器，这样三者就都绑定在了一起，成为了一个整体。

 

三、IIC设备的操作

 

系统对IIC设备的操作是在at24_probe函数完成的：

static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)

{

       structat24_platform_data chip;

       boolwritable;

       intuse_smbus = 0;

       structat24_data *at24;

       interr;

       unsignedi, num_addresses;

       kernel_ulong_tmagic;

 

       if(client->dev.platform_data) {

              chip= *(struct at24_platform_data *)client->dev.platform_data;

       }else {

              if(!id->driver_data) {

                     err= -ENODEV;

                     gotoerr_out;

              }

              magic = id->driver_data;

              chip.byte_len= BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));

              magic>>= AT24_SIZE_BYTELEN;

              chip.flags= magic & AT24_BITMASK(AT24_SIZE_FLAGS);

              /*

               * This is slow, but we can't know all eeproms,so we better

               * play safe. Specifying custom eeprom-typesvia platform_data

               * is recommended anyhow.

               */

              chip.page_size= 1;

 

              /*update chipdata if OF is present */

              at24_get_ofdata(client,&chip);

 

              chip.setup= NULL;

              chip.context= NULL;

       }

 

       //判断IIC设备（这里指的就是eeprom）容量是否为2的次幂

       if(!is_power_of_2(chip.byte_len))

              dev_warn(&client->dev,

                     "byte_lenlooks suspicious (no power of 2)!\n");

       //判断eeprom的每页的大小

       if(!chip.page_size) {

              dev_err(&client->dev,"page_size must not be 0!\n");

              err= -EINVAL;

              gotoerr_out;

       }

       //判断eeprom每页的大小是否为2的次幂

       if(!is_power_of_2(chip.page_size))

              dev_warn(&client->dev,

                     "page_sizelooks suspicious (no power of 2)!\n");

 

       /*Use I2C operationsunless we're stuck with SMBus extensions. */

       if(!i2c_check_functionality(client->adapter,I2C_FUNC_I2C)) {

              if(chip.flags & AT24_FLAG_ADDR16) {

                     err= -EPFNOSUPPORT;

                     gotoerr_out;

              }

              if(i2c_check_functionality(client->adapter,

                            I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {

                     use_smbus= I2C_SMBUS_I2C_BLOCK_DATA;

              }else if (i2c_check_functionality(client->adapter,

                            I2C_FUNC_SMBUS_READ_WORD_DATA)) {

                     use_smbus= I2C_SMBUS_WORD_DATA;

              }else if (i2c_check_functionality(client->adapter,

                            I2C_FUNC_SMBUS_READ_BYTE_DATA)) {

                     use_smbus= I2C_SMBUS_BYTE_DATA;

              }else {

                     err= -EPFNOSUPPORT;

                     gotoerr_out;

              }

       }

 

       if(chip.flags & AT24_FLAG_TAKE8ADDR)

              num_addresses= 8;

       else

              num_addresses=    DIV_ROUND_UP(chip.byte_len,

                     (chip.flags &AT24_FLAG_ADDR16) ? 65536 : 256);

 

       at24= kzalloc(sizeof(struct at24_data) +

              num_addresses* sizeof(struct i2c_client *),GFP_KERNEL);

       if(!at24) {

              err= -ENOMEM;

              gotoerr_out;

       }

 

       mutex_init(&at24->lock);

       at24->use_smbus= use_smbus;

       at24->chip= chip;

       at24->num_addresses= num_addresses;

 

       /*

        * Export the EEPROM bytes through sysfs, sincethat's convenient.

        * By default, only root should see the data(maybe passwords etc)

        */

       //下面是定义一些关于sysfs的属性

       sysfs_bin_attr_init(&at24->bin);

       at24->bin.attr.name ="eeprom";          //名称

       at24->bin.attr.mode = chip.flags &AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;

       at24->bin.read= at24_bin_read;          //读操作

       at24->bin.size = chip.byte_len;

 

       at24->macc.read= at24_macc_read;

 

       writable= !(chip.flags & AT24_FLAG_READONLY);

       if(writable) {

              if(!use_smbus || i2c_check_functionality(client->adapter,

                            I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {

 

                     unsignedwrite_max = chip.page_size;

 

                     at24->macc.write= at24_macc_write;

 

                     at24->bin.write =at24_bin_write;               //写操作

                     at24->bin.attr.mode|= S_IWUSR;

 

                     if(write_max > io_limit)

                            write_max= io_limit;

                     if(use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)

                            write_max= I2C_SMBUS_BLOCK_MAX;

                     at24->write_max= write_max;

 

                     /*buffer (data + address at the beginning) */

                     at24->writebuf= kmalloc(write_max + 2, GFP_KERNEL);

                     if(!at24->writebuf) {

                            err= -ENOMEM;

                            gotoerr_struct;

                     }

              }else {

                     dev_warn(&client->dev,

                            "cannotwrite due to controller restrictions.");

              }

       }

 

       at24->client[0]= client;

 

       /*use dummy devices for multiple-address chips */

       for (i = 1; i < num_addresses; i++){

              at24->client[i]= i2c_new_dummy(client->adapter,

                                   client->addr+ i);

              if(!at24->client[i]) {

                     dev_err(&client->dev,"address 0x%02x unavailable\n",

                                   client->addr+ i);

                     err= -EADDRINUSE;

                     gotoerr_clients;

              }

       }

 

       //为sysfs创建二进制文件

       err= sysfs_create_bin_file(&client->dev.kobj, &at24->bin);

       if(err)

              gotoerr_clients;

 

       i2c_set_clientdata(client, at24);

 

       dev_info(&client->dev,"%zu byte %s EEPROM, %s, %u bytes/write\n",

              at24->bin.size,client->name,

              writable? "writable" : "read-only", at24->write_max);

       if(use_smbus == I2C_SMBUS_WORD_DATA||

           use_smbus == I2C_SMBUS_BYTE_DATA) {

              dev_notice(&client->dev,"Falling back to %s reads, "

                        "performance will suffer\n",use_smbus ==

                        I2C_SMBUS_WORD_DATA? "word" : "byte");

       }

 

       /*export data to kernel code */

       if(chip.setup)

              chip.setup(&at24->macc,chip.context);

 

       return0;

 

err_clients:

       for(i = 1; i < num_addresses; i++)

              if(at24->client[i])

                     i2c_unregister_device(at24->client[i]);

 

       kfree(at24->writebuf);

err_struct:

       kfree(at24);

err_out:

       dev_dbg(&client->dev,"probe error %d\n", err);

       returnerr;

}

 

在这里，读文件的函数为at24_bin_read，它又调用了at24_read函数，最后又调用at24_eeprom_read函数；同样的，写文件的函数为at24_bin_write，它又调用了at24_write函数，最后又调用at24_eeprom_write函数。at24_eeprom_read和at24_eeprom_write最终都要调用i2c_transfer函数，来真正完成对AT24C02的读写操作。

 

i2c_transfer函数已经在上一篇文章分析过了，这里就不再重复。

 

四、应用程序

 

基于sysfs文件系统的IIC子系统的整个过程就介绍完了，我们来验证一下。

 

系统为IIC创建的sysfs文件系统在/sys/bus/i2c/devices/0-0050/目录下，该目录下有一个eeprom文件，只要对该文件进行操作，就可以实现对eeprom的读写，我们来测试一下：

[root@zhaocj /]#hexdump  -C  /sys/bus/i2c/devices/0-0050/eeprom

00000000  61 62 63 0a 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f |abc.............|

00000010  19 95 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f  |................|

00000020  ee 71 67 23 42 25 26 27 00 9f 03 5a 2e 67 89 10  |.qg#B%&'...Z.g..|

00000030  a9 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 3e 3f  |.123456789:;<=>?|

00000040  40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f  |@ABCDEFGHIJKLMNO|

00000050  50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f  |PQRSTUVWXYZ[\]^_|

00000060  60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f  |`abcdefghijklmno|

00000070  70 71 72 73 74 75 76 77 78 79 7a 7b 7c 7d 7e 7f  |pqrstuvwxyz{|}~.|

00000080  80 81 82 83 84 85 86 87 88 89 8a 8b 8c 8d 8e 8f  |................|

00000090  90 91 92 93 94 95 96 97 98 99 9a 9b 9c 9d 9e 9f  |................|

000000a0  a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 aa ab acad ae af  |................|

000000b0  b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 ba bb bc bd be bf  |................|

000000c0  c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 ca cb cccd ce cf  |................|

000000d0  d0 d1 d2 d3 d4 d5 d6 d7 d8 d9 da db dc dd de df  |................|

000000e0  e0 e1 e2 e3 e4 e5 e6 e7 03 5a 2e 67 8910 ee 9f |.........Z.g....|

000000f0  f0 f1 f2 f3 f4 f5 f6 f7 f8 f9 fa fb fcfd fe ff  |................|

 

在命令行下输入上述命令，就会把eeprom中的地址的内容全部呈现出来，cat也具有同样的功能。我们也可以通过echo修改内容：

[root@zhaocj /]#echo  "zcj" >> /sys/bus/i2c/devices/0-0050/eeprom

[root@zhaocj /]#cat   /sys/bus/i2c/devices/0-0050/eeprom

zcj

 

 

��qg#B%&'�Z.g��123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~������������������������������������������������������������������������������������������������������Z.g�������������������

 

下面我们写一段应用程序来实现对eeprom的读写，完成的任务是先从地址为0x40处开始写入数据，然后再从相同的位置读取：

 

#include<stdio.h>

#include<stdlib.h>

#include<sys/types.h>

#include<sys/stat.h>

#include<fcntl.h>

#include<string.h>

 

int main(void){

       intfd, size, len, i;

       char buf[50]=;

       char *bufw="Hi,this is an eepromtest!";

 

       len=strlen(bufw);

 

       fd= open("/sys/bus/i2c/devices/0-0050/eeprom",O_RDWR);

       if(fd< 0){

              printf("####i2c test device open failed####/n");

              return(-1);

       }

      //写操作

       lseek(fd,0x40,SEEK_SET);         //地址是0x40

       if((size=write(fd,bufw, len))<0){

              printf("write error\n");

              return 1;

       }

       printf("writeok\n");

       //读操作

       lseek(fd,0x40, SEEK_SET);

       if((size=read(fd,buf,len))<0){

              printf("readerror\n");

              return 1;

       }

       printf("readok\n");

       for(i=0; i< len; i++)

printf("buff[%d]=%x\n",i, buf[i]);

 

       close(fd);

       return 0;

}

 

仅从撰写IIC应用程序来看，sysfs的方法要更简单一些，而且不涉及硬件的知识；而devfs的方法要灵活一些。