Linux I2C驱动分析与实现(二)
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通过上篇《Linux I2C驱动分析与实现(二)》，我们对Linux子系统已经不陌生,那么如何实现I2C驱动呢？
编写客户驱动的方法
在内核中有两种方式的i2c客户驱动的编写方法，一种叫legacy传统方式，另一种是newstyle方式. 前
一种legacy是一种旧式的方法，在2.6内核以后的标准驱动模型编写中逐渐被newstyle方式取代。本文编程实例是基于newstyle方式的来实现at24c02的驱
动。
客户驱动程序开发的一般步骤
(1)注册板载i2c设备信息
(2)定义i2c驱动设备id
(3)定义i2c_driver结构并完成其相应函数
(4)模块初始化时添加/撤销时删除i2c_driver
(5)/dev entry 访问方法 /sysfs访问方法
客户设备驱动开发实例
内核为linux-2.6.30.4
基于arm9 S3c2440平台
开发一个at24c02 eeprom的客户驱动
开发一个应用程序访问I2C设备
-----------------------------------------------------------------
根据开发客户驱动程序步骤实现对i2c设备at24c02的读写操作。
(分析at24c02 datasheet)
(1)注册板载信息
在mach-smdk2440.c文件中静态声明一个I2C设备
static struct i2c_board_info i2c_devices[] __initdata = {
{I2C_BOARD_INFO("24c02", 0x50), },
{}
};
在smdk2440_machine_init()函数中，向总线注册I2C设备信息：
i2c_register_board_info(0,i2c_devices,ARRAY_SIZE(i2c_devices));
(2)定义i2c驱动设备id：
static struct i2c_device_id foo_idtable[] = {
{ “24c01", 0x51 },
{“20402”，0x50 },
{}
};
(3)定义i2c_driver结构并完成其相应函数:
static struct i2c_driver my_i2c_driver = {
.driver = {
.name = "i2c_demo",
.owner = THIS_MODULE,
},
.probe = my_i2c_probe,
.remove = my_i2c_remove,
.id_table = my_ids,
};
(4)模块初始化时添加/撤销时删除i2c_driver
static int __init my_i2c_client(void)
{
return i2c_add_driver(&my_i2c_driver);
}
static void __exit my_i2c_exit(void)
{
i2c_del_driver(&my_i2c_driver);
}
(5)使用/dev entry 访问方法
注册字符设备
register_chrdev(I2C_MAJOR,DEVICE_NAME,&i2c_fops); 创建类class_create(THIS_MODULE, DEVICE_NAME); 在/dev下创建设备节点 device_create(my_dev_class, &client->dev,MKDEV(I2C_MAJOR, 0), NULL, DEVICE_NAME);
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代码测试结果：
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/i2c.h>
#include <linux/i2c-dev.h>
#include <linux/smp_lock.h>
#include <linux/jiffies.h>
#include <asm/uaccess.h>
#include <linux/delay.h>
#define DEBUG 1
#ifdef DEBUG
#define dbg(x...) printk(x)
#else
#define dbg(x...) (void)(0)
#endif
#define I2C_MAJOR 89
#define DEVICE_NAME "at24c02"
static struct class *my_dev_class;
static struct i2c_client *my_client;
static struct i2c_driver my_i2c_driver;
static struct i2c_device_id my_ids[] = {
{"24c01",0x50},
{"24c02",0x50},
{"24c08",0x50},
{}
};
MODULE_DEVICE_TABLE(i2c,my_ids);
static int my_i2c_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
int res;
struct device *dev;
dbg("probe:name = %s,flag =%d,addr = %d,adapter = %d,driver = %s\n",client->name,
client->flags,client->addr,client->adapter->nr,client->driver->driver.name );
dev = device_create(my_dev_class, &client->dev,
MKDEV(I2C_MAJOR, 0), NULL,
DEVICE_NAME);
if (IS_ERR(dev))
{
dbg("device create error\n");
goto out;
}
my_client = client;
return 0;
out:
return -1;
}
static int my_i2c_remove(struct i2c_client *client)
{
dbg("remove\n");
return 0;
}
static ssize_t at24c02_read(struct file *fd, char *buf, ssize_t count, loff_t *offset)
{
char *tmp;
int ret;
char data_byte;
char reg_addr = 0,i;
struct i2c_client *client = (struct i2c_client*) fd->private_data;
struct i2c_msg msgs[2];
dbg("read:count = %d,offset = %ld\n",count,*offset);
tmp = kmalloc(count,GFP_KERNEL);
if (!tmp)
{
dbg("malloc error in read function\n");
goto out;
}
reg_addr = *offset;
msgs[0].addr = client->addr;
msgs[0].flags = client->flags & (I2C_M_TEN|I2C_CLIENT_PEC) ;
msgs[0].len = 1;
msgs[0].buf = (char *)®_addr;
msgs[1].addr= client->addr;
msgs[1].flags = client->flags & (I2C_M_TEN|I2C_CLIENT_PEC);
msgs[1].flags |= I2C_M_RD;
msgs[1].len = count;
msgs[1].buf = (char*)tmp;
ret = i2c_transfer(client->adapter,&msgs,2);
if (ret != 2)
goto out;
if (copy_to_user(buf, tmp, count))
goto out;
kfree(tmp);
return count;
out:
kfree(tmp);
return -1;
}
static int at24c02_ioctl(struct file *fd, unsigned int cmd, unsigned long arg)
{
dbg("ioctl code ...\n");
return 0;
}
static ssize_t at24c02_write(struct file *fd, char *buf, ssize_t count, loff_t *offset)
{
int ret,i;
char *tmp;
int errflg;
struct i2c_msg msg;
struct i2c_client *client = (struct i2c_client*) fd->private_data;
char tmp_data[2];
dbg("write:count = %d,offset = %ld\n",count,*offset);
tmp = kmalloc(count, GFP_KERNEL);
if (!tmp)
goto out;
if (copy_from_user(tmp, buf, count))
goto out;
msg.addr = client->addr;
msg.flags = client->flags & (I2C_M_TEN | I2C_CLIENT_PEC);
for (i = 0; i < count; i++) {
msg.len = 2;
tmp_data[0] = *offset + i;
tmp_data[1] = tmp[i];
msg.buf = tmp_data;
ret = i2c_transfer(client->adapter,&msg,1);
if (ret != 1)
goto out;
msleep(1);
}
kfree(tmp);
return ((ret == 1) ? count:ret);
out:
kfree(tmp);
return -1;
}
static int at24c02_open(struct inode *inode, struct file *fd)
{
fd->private_data =(void*)my_client;
return 0;
}
static int at24c02_release(struct inode *inode, struct file *fd)
{
dbg("release\n");
fd->private_data = NULL;
return 0;
}
static const struct file_operations i2c_fops = {
.owner = THIS_MODULE,
.open = at24c02_open,
.read = at24c02_read,
.write = at24c02_write,
.unlocked_ioctl = at24c02_ioctl,
.release = at24c02_release,
};
static struct i2c_driver my_i2c_driver = {
.driver = {
.name = "i2c_demo",
.owner = THIS_MODULE,
},
.probe = my_i2c_probe,
.remove = my_i2c_remove,
.id_table = my_ids,
};
static int __init my_i2c_init(void)
{
int res;
res = register_chrdev(I2C_MAJOR,DEVICE_NAME,&i2c_fops);
if (res)
{
dbg("register_chrdev error\n");
return -1;
}
my_dev_class = class_create(THIS_MODULE, DEVICE_NAME);
if (IS_ERR(my_dev_class))
{
dbg("create class error\n");
unregister_chrdev(I2C_MAJOR, DEVICE_NAME);
return -1;
}
return i2c_add_driver(&my_i2c_driver);
}
static void __exit my_i2c_exit(void)
{
unregister_chrdev(I2C_MAJOR, DEVICE_NAME);
class_destroy(my_dev_class);
i2c_del_driver(&my_i2c_driver);
}
MODULE_AUTHOR("itspy<[email protected]>");
MODULE_DESCRIPTION("i2c client driver demo");
MODULE_LICENSE("GPL");
module_init(my_i2c_init);
module_exit(my_i2c_exit);