I2C驱动2

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。