linux驱动——杂项设备

    杂项设备也是在嵌入式系统中用得比较多的一种设备驱动。在 Linux 内核的include/linux目录下有Miscdevice.h文件，要把自己定义的misc device从设备定义在这里。其实是因为这些字符设备不符合预先确定的字符设备范畴，所有这些设备采用主编号10 ，一起归于misc device，其实misc_register就是用主标号10调用register_chrdev()的。也就是说，misc设备其实也就是特殊的字符设备，可自动生成设备节点。

 

\include\linux\miscdevice.h

在这个头文件中主要是misc(混合)设备注册和注销：
其它类型－－－不能严格划分的设备类型，也叫混合类型
有：

#ifndef _LINUX_MISCDEVICE_H
#define _LINUX_MISCDEVICE_H
#include <linux/module.h>
#include <linux/major.h>
#define PSMOUSE_MINOR 1
#define MS_BUSMOUSE_MINOR 2
#define ATIXL_BUSMOUSE_MINOR 3
/*#define AMIGAMOUSE_MINOR 4 FIXME OBSOLETE */
#define ATARIMOUSE_MINOR 5
#define SUN_MOUSE_MINOR 6
#define APOLLO_MOUSE_MINOR 7
#define PC110PAD_MINOR 9
/*#define ADB_MOUSE_MINOR 10 FIXME OBSOLETE */
#define WATCHDOG_MINOR 130 /* Watchdog timer */
#define TEMP_MINOR 131 /* Temperature Sensor */
#define RTC_MINOR 135
#define EFI_RTC_MINOR 136 /* EFI Time services */
#define SUN_OPENPROM_MINOR 139
#define DMAPI_MINOR 140 /* DMAPI */
#define NVRAM_MINOR 144
#define SGI_MMTIMER 153
#define STORE_QUEUE_MINOR 155
#define I2O_MINOR 166
#define MICROCODE_MINOR 184
#define TUN_MINOR 200
#define MWAVE_MINOR 219 /* ACP/Mwave Modem */
#define MPT_MINOR 220
#define MPT2SAS_MINOR 221
#define HPET_MINOR 228
#define FUSE_MINOR 229
#define KVM_MINOR 232
#define MISC_DYNAMIC_MINOR 255
struct device;
struct miscdevice {
 int minor;/*次设备号*/
 const char *name;/*misc设备名*/
 const struct file_operations *fops;/*misc设备文件操作结构体*/
 struct list_head list;
 struct device *parent;
 struct device *this_device;
 const char *nodename;
 mode_t mode;
};

minor：所有的misc设备共用一个主设备号，所以注册misc设备时只要次
设备号就可以了。利用次设备号来区分设备的。

misc设备注册：
extern int misc_register(struct miscdevice * misc);
misc设备注销：
extern int misc_deregister(struct miscdevice * misc);
drivers/char/misc.c

int misc_register(struct miscdevice * misc)
{
   struct miscdevice *c;
   dev_t dev;
   int err = 0;

   down(&misc_sem);
   list_for_each_entry(c, &misc_list, list) {
     if (c->minor == misc->minor) {
        up(&misc_sem);
        return -EBUSY;
     }
   }

   if (misc->minor == MISC_DYNAMIC_MINOR) {
      int i = DYNAMIC_MINORS;
      while (--i >= 0)
        if ( (misc_minors[i>>3] & (1 << (i&7))) == 0)
             break;
      if (i<0) {
        up(&misc_sem);
        return -EBUSY;
      }
      misc->minor = i;
   }

   if (misc->minor < DYNAMIC_MINORS)
      misc_minors[misc->minor >> 3] |= 1 << (misc->minor & 7);
   dev = MKDEV(MISC_MAJOR, misc->minor);

   misc->class = class_device_create(misc_class, NULL, dev, misc->dev,"%s", misc->name);
   if (IS_ERR(misc->class)) {
       err = PTR_ERR(misc->class);
      goto out;
   }
/*
* Add it to the front, so that later devices can "override"
* earlier defaults
*/
   list_add(&misc->list, &misc_list);
out:
    up(&misc_sem);
    return err;
}
/**
* misc_deregister - unregister a miscellaneous device
* @misc: device to unregister
*
* Unregister a miscellaneous device that was previously
* successfully registered with misc_register(). Success
* is indicated by a zero return, a negative errno code
* indicates an error.
*/

int misc_deregister(struct miscdevice * misc)
{
   int i = misc->minor;
   if (list_empty(&misc->list))
       return -EINVAL;
   down(&misc_sem);
   list_del(&misc->list);
   class_device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
   if (i < DYNAMIC_MINORS && i>0) {
       misc_minors[i>>3] &= ~(1 << (misc->minor & 7));
   }
   up(&misc_sem);
   return 0;
}
EXPORT_SYMBOL(misc_register);
EXPORT_SYMBOL(misc_deregister);
static int __init misc_init(void)
{
#ifdef CONFIG_PROC_FS
   struct proc_dir_entry *ent;
   ent = create_proc_entry("misc", 0, NULL);
   if (ent)
      ent->proc_fops = &misc_proc_fops;
#endif
   misc_class = class_create(THIS_MODULE, "misc");
   if (IS_ERR(misc_class))
      return PTR_ERR(misc_class);

   if (register_chrdev(MISC_MAJOR,"misc",&misc_fops)) {
       printk("unable to get major %d for misc devices/n",MISC_MAJOR);
       class_destroy(misc_class);
       return -EIO;
   }
    return 0;
}
subsys_initcall(misc_init);