第15章　Linux I2C核心、总线与设备驱动之I2C设备驱动实例-优快云博客

15.6　AT24xx EEPROM（电可擦除可编程只读存储器）的I2C设备（外设）驱动实例

drivers/misc/eeprom/at24.c文件支持大多数I2C接口的EEPROM，正如之前所述，一个具体的I2C设备驱动由i2c_driver的形式来组织，用于将设备挂接在I2C总线，组织好以后，再完成设备本身所属类型的驱动。对于EEPROM，设备本身的驱动以bin_attribute二进制sysfs节点形式呈现。

代码清单15.25　AT24xx EEPROM驱动

struct at24_data {
struct at24_platform_data chip;
struct memory_accessor macc;
int use_smbus;
/*
* Lock protects against activities from other Linux tasks,
* but not from changes by other I2C masters.
*/
struct mutex lock;
struct bin_attribute bin;

u8 *writebuf;
unsigned write_max;
unsigned num_addresses;
/*
* Some chips tie up multiple I2C addresses; dummy devices reserve
* them for us, and we'll use them with SMBus calls.
*/
struct i2c_client *client[];

};

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) },
......
{ "at24", 0 },
{ /* END OF LIST */ }
};

MODULE_DEVICE_TABLE(i2c, at24_ids);

static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
unsigned offset, size_t count)
{
struct i2c_msg msg[2];
u8 msgbuf[2];
struct i2c_client *client;
unsigned long timeout, read_time;
int status, i;

memset(msg, 0, sizeof(msg));
client = at24_translate_offset(at24, &offset);

if (count > io_limit)
count = io_limit;

switch (at24->use_smbus) {
case I2C_SMBUS_I2C_BLOCK_DATA:
/* Smaller eeproms can work given some SMBus extension calls */
if (count > I2C_SMBUS_BLOCK_MAX)
count = I2C_SMBUS_BLOCK_MAX;
break;
case I2C_SMBUS_WORD_DATA:
count = 2;
break;
case I2C_SMBUS_BYTE_DATA:
count = 1;
break;
default:

i = 0;
if (at24->chip.flags & AT24_FLAG_ADDR16)
msgbuf[i++] = offset >> 8;
msgbuf[i++] = offset;
msg[0].addr = client->addr;
msg[0].buf = msgbuf;
msg[0].len = i;
msg[1].addr = client->addr;
msg[1].flags = I2C_M_RD;
msg[1].buf = buf;
msg[1].len = count;
}

timeout = jiffies + msecs_to_jiffies(write_timeout);
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