自动创建字符设备，不需mknod

自动创建设备文件
1.自动创建设备文件的流程
字符设备驱动模块 --》创建一个设备驱动class--->创建属于class的device--->调用mdev工具(自动完成)--> 生成设备文件

mdev工具会根据/sys下的class找到相对应的device，然后根据device创建设备文件

class /sys/class
device /sys/device

1.1创建class /注销class

struct class * class_create(struct module *owner,const char *name);
参数:
struct module *owner---> class属于哪些一个module --->THIS_MODULE
const char *name --->自定义的类名.

返回值:
NULL -->失败

void class_destroy(struct class * cls)

例:
struct class *led_class=class_create(THIS_MODULE,"led_class");
class_destroy(led_class)

1.2创建device /注销
struct device *device_create(struct class *class, struct device *parent,
dev_t devt, void *drvdata, const char *fmt, ...)
参数:
struct class *class --->当前device属于那个class
struct device *parent --->device的parent,一般为NULL
dev_t devt --->设备号
void *drvdata --->设备的私有数据，一般为NULL
const char *fmt ---》 device的名字，也就是设备文件名

返回值:
struct device *
NULL -->失败

void device_destroy(struct class * class,dev_t devt);

struct device *dp=device_create(led_class,NULL,dev_no,NULL,"led_drv") ---> /dev/led_drv (字符设备)
if(dp==NULL)
{

}

 #include<linux/module.h>
 #include<linux/kernel.h>
 #include<linux/cdev.h>
 #include<linux/fs.h>
 #include<linux/kdev_t.h>
 #include<linux/types.h>
 #include<linux/uaccess.h>
 #include<linux/string.h>
 #include<linux/ioport.h>
 #include<asm/io.h>
 #include<linux/init.h>
 #include<linux/device.h>
 #define  GPJ2CON_PA 0xe0200280
 #define  GPJ2DAT_PA 0xe0200280
 unsigned int *GPJ2CON_VA;
 unsigned int *GPJ2DAT_VA;
 struct cdev chrdev;
 struct resource *res;
 struct class *cla;
 struct device *dev;
 unsigned int TestMajor=;
 unsigned int TestMinor=;
 dev_t dev_no;
 int ret;

 int testopen(struct inode *inode,struct file *file)
 {
     unsigned int a = ioread32(GPJ2CON_VA);
     a |= 0x1111;
     iowrite32(a,GPJ2CON_VA);
     printk("cdev init\n");
     return ;

 }
 ssize_t testwrite(struct file *file, const char __user *usr, size_t len, loff_t *off)
 {
     unsigned int a;

     copy_from_user(&a,usr,len);
     iowrite32(a,GPJ2DAT_VA);

 }
 ssize_t testread(struct file *file, char __user *usr, size_t len, loff_t *off)
 {
     unsigned int a = ioread32(GPJ2DAT_VA);
     copy_to_user(usr,&a,len);

 }
 int testrelease(struct inode *inode, struct file *file)
 {
     printk("close\n");
     return ;

 }

 struct file_operations fops=
 {
     .owner=THIS_MODULE,
     .open = testopen,
     .write = testwrite,
     .read = testread,
     .release = testrelease,
 };
 static int __init test_init(void)
 {
     dev_no = MKDEV(TestMajor,TestMinor);
     if(dev_no>)
     {
         ret = register_chrdev_region(dev_no,,"chrdev_test");
     }
     else
     {
         alloc_chrdev_region(&dev_no,,,"chrdev_test");
     }
     if(ret<)
     {
         return ret;
     }
     cdev_init(&chrdev,&fops);
     chrdev.owner=THIS_MODULE;
     cdev_add(&chrdev,dev_no,);
     res = request_mem_region(GPJ2CON_PA,,"gpj2_led");
     GPJ2CON_VA = ioremap(GPJ2CON_PA,);
     GPJ2DAT_VA = GPJ2CON_VA + ;
     cla = class_create(THIS_MODULE,"led_class");
     if(cla == NULL)
     {
         printk("class_creat() error!\n");
     }
     dev = device_create(cla,NULL,dev_no,NULL,"chrdev_test");
     if(dev == NULL)
     {
         printk("device_creat() error!\n");
     }

     return ;
 }

 static int __exit test_exit(void)
 {
     unregister_chrdev_region(dev_no,);
     cdev_del(&chrdev);
     iounmap(GPJ2CON_VA);
     release_mem_region(GPJ2CON_PA,);
     device_destroy(cla,dev_no);
     class_destroy(cla);
     return ;
 }

 module_init(test_init);
 module_exit(test_exit);

 MODULE_AUTHOR("FENG");
 MODULE_DESCRIPTION("the first module of char drivers");
 MODULE_LICENSE("GPL");
 MODULE_VERSION("V1.0");