简介
杂项设备驱动，就是最简单的字符设备驱动，通常嵌套在platform总线驱动中实现复杂的驱动
主设备号都为10，不同的设备使用不同的从设备号
MISC设备驱动用于解决字符设备驱动不断增加设备号紧张的问题
MISC设备会自动创建cdev，不需要以前那样手动创建
采用MISC设备驱动可以简化字符设备驱动的编写
驱动框架
我们需要向Linux内核注册一个miscdevice设备，miscdevice是一个结构体
miscdevice
定义在\linux\miscdevice.h中，描述了misc设备
struct miscdevice {
int minor;
const char *name;
const struct file_operations *fops;
struct list_head list;
struct device *parent;
struct device *this_device;
const struct attribute_group **groups;
const char *nodename;
umode_t mode;
};
我们需要设置minor、name、fops这三个成员变量
\linux\miscdevice.h中也预定义了一些子设备号，可以从中指定也可以自己定义
#define PSMOUSE_MINOR 1
#define MS_BUSMOUSE_MINOR 2 /* unused */
#define ATIXL_BUSMOUSE_MINOR 3 /* unused */
/*#define AMIGAMOUSE_MINOR 4 FIXME OBSOLETE */
#define ATARIMOUSE_MINOR 5 /* unused */
#define SUN_MOUSE_MINOR 6 /* unused */
#define APOLLO_MOUSE_MINOR 7 /* unused */
#define PC110PAD_MINOR 9 /* unused */
/*#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 VHCI_MINOR 137
#define SUN_OPENPROM_MINOR 139
#define DMAPI_MINOR 140 /* unused */
#define NVRAM_MINOR 144
#define SGI_MMTIMER 153
#define STORE_QUEUE_MINOR 155 /* unused */
#define I2O_MINOR 166
#define MICROCODE_MINOR 184
#define VFIO_MINOR 196
#define TUN_MINOR 200
#define CUSE_MINOR 203
#define MWAVE_MINOR 219 /* ACP/Mwave Modem */
#define MPT_MINOR 220
#define MPT2SAS_MINOR 221
#define MPT3SAS_MINOR 222
#define UINPUT_MINOR 223
#define MISC_MCELOG_MINOR 227
#define HPET_MINOR 228
#define FUSE_MINOR 229
#define KVM_MINOR 232
#define BTRFS_MINOR 234
#define AUTOFS_MINOR 235
#define MAPPER_CTRL_MINOR 236
#define LOOP_CTRL_MINOR 237
#define VHOST_NET_MINOR 238
#define UHID_MINOR 239
#define MISC_DYNAMIC_MINOR 255
与字符设备的对比
注册
设置好miscdevice结构体后使用misc_register向系统注册一个MISC设备
int misc_register(struct miscdevice *misc);
原先我们需要
alloc_chrdev_region(); /* 申请设备号 */
cdev_init(); /* 初始化cdev */
cdev_add(); /* 添加cdev */
class_create(); /* 创建类 */
device_create(); /* 创建设备 */
卸载
当我们卸载驱动的时候调用misc_deregister来注销MISC设备
int misc_deregister(struct miscdevice *misc);
原先我们需要
cdev_del(); /* 删除cdev */
unregister_chrdev_region(); /* 注销设备号 */
device_destroy(); /* 删除设备 */
class_destroy(); /* 删除类 */
实验代码与分析
实验代码
#include <linux/init.h>
#include <linux/ide.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/moduleparam.h>
#include <linux/stat.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/gpio.h>
#include <linux/errno.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <linux/semaphore.h>
#include <linux/timer.h>
#include <linux/of_irq.h>
#include <linux/irq.h>
#include <linux/platform_device.h>
#include <linux/miscdevice.h>
#include <asm/io.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#define MISCBEEP_MINOR 144
#define MISCBEEP_NAME "miscbeep"
#define BEEPOFF 0
#define BEEPON 1
struct miscbeep_dev {
dev_t devid;
struct cdev cdev;
struct class *class;
struct device *device;
struct device_node *nd;
int beep_gpio;
};
struct miscbeep_dev miscbeep;
static int miscbeep_open(struct inode *inode,struct file *filp)
{
printk(KERN_EMERG "miscbeep_open enter!\n");
filp->private_data = &miscbeep;
return 0;
}
static ssize_t miscbeep_write(struct file *filp,const char __user *buf,size_t cnt,loff_t *offt)
{
int retvalue;
unsigned char databuf[2];
unsigned char beepstat;
struct miscbeep_dev *dev = (struct miscbeep_dev *)filp->private_data;
printk(KERN_EMERG "miscbeep_write enter!\n");
retvalue = copy_from_user(databuf, buf, cnt);
if(retvalue < 0)
{
printk(KERN_EMERG "kernel write failed!\n");
return -EFAULT;
}
beepstat = databuf[0];
if(beepstat == BEEPON)
{
gpio_set_value(dev->beep_gpio, 0);
}
else if(beepstat == BEEPOFF)
{
gpio_set_value(dev->beep_gpio, 1);
}
return 0;
}
static struct file_operations miscbeep_fops = {
.owner = THIS_MODULE,
.open = miscbeep_open,
.write = miscbeep_write,
};
static struct miscdevice beep_miscdev = {
.minor = MISCBEEP_MINOR,
.name = MISCBEEP_NAME,
.fops = &miscbeep_fops,
};
static int miscbeep_probe(struct platform_device *dev)
{
int ret = 0;
printk(KERN_EMERG "miscbeep_probe enter!\n");
/*1.Get device node*/
miscbeep.nd = of_find_node_by_path("/beep");
if(miscbeep.nd == NULL)
{
printk(KERN_EMERG "beep node not find!\n");
return -EINVAL;
}
/*2.get gpio property*/
miscbeep.beep_gpio = of_get_named_gpio(miscbeep.nd, "beep-gpio", 0);
if(miscbeep.beep_gpio < 0)
{
printk(KERN_EMERG "can't get beep-gpio!\n");
return -EINVAL;
}
/*3.set gpio output,output high default,close beep*/
ret = gpio_direction_output(miscbeep.beep_gpio, 1);
if(ret < 0)
{
printk(KERN_EMERG "can't set beep-gpio!\n");
}
ret = misc_register(&beep_miscdev);
if(ret < 0)
{
printk(KERN_EMERG "misc device register failed!\n");
return -EINVAL;
}
return 0;
}
static int miscbeep_remove(struct platform_device *dev)
{
/*close beep*/
gpio_set_value(miscbeep.beep_gpio, 1);
/*deregister misc driver*/
misc_deregister(&beep_miscdev);
return 0;
}
static const struct of_device_id miscbeep_of_match[] = {
{ .compatible = "atkalpha-beep"},
{ /**/ }
};
static struct platform_driver miscbeep_driver = {
.driver = {
.name = "im6ul-beep",
.of_match_table = miscbeep_of_match,
},
.probe = miscbeep_probe,
.remove = miscbeep_remove,
};
static int __init miscdriver_init(void)
{
return platform_driver_register(&miscbeep_driver);
}
static void __exit miscdriver_exit(void)
{
platform_driver_unregister(&miscbeep_driver);
}
module_init(miscdriver_init);
module_exit(miscdriver_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("GYY");
代码分析
- 总体来看我们可以发现，还是platform驱动的结构，需要定义platform_driver ，在init和exit函数中，做的是platform设备的注册和卸载
- 我们定义了miscbeep_dev 结构体来表示一个我们的设备，这里其实值用到了设备树节点nd和GPIO用于操作蜂鸣器
- 我们还需要定义一个miscdevice结构体类型的变量代表misc设备
- 与之前platform驱动的区别之处就在于probe函数和remove函数中所做的事情，在probe函数中，我们只做了GPIO的获取以及初始化，然后调用misc_register来注册MISC设备，在remove函数中我们调用misc_deregister来卸载MISC设备
- 在open和write函数中的操作就是和普通驱动中是相同的
