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linux驱动开发学习四：中断与时钟

代码如下:
#include <linux/module.h>
#include <linux/fs.h>
#include  <linux/mm.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include<linux/jiffies.h>
#include<linux/timer.h>

#define SECOND_MAJOR  260

static int second_major=SECOND_MAJOR;

module_param(second_major,int,S_IRUGO);

struct second_dev{
    struct cdev cdev;
    atomic_t counter;
    struct timer_list s_timer;
};

static struct second_dev *second_devp;

static void second_timer_handler(struct timer_list *s)
{
    mod_timer(&second_devp->s_timer,jiffies+HZ);
    atomic_inc(&second_devp->counter);
    printk(KERN_INFO "current jiffies is %ld\n",jiffies);
}


static int second_open(struct inode *ins_timerode,struct file *filep)
{
    timer_setup(&second_devp->s_timer,second_timer_handler,0);　
    //second_devp->s_timer.function=&second_timer_handler;
    second_devp->s_timer.expires=jiffies+HZ;
    add_timer(&second_devp->s_timer);
    atomic_set(&second_devp->counter,0);
    return 0;
}

static int second_release(struct inode *inode,struct file *filep)
{
    del_timer(&second_devp->s_timer);
    return 0;
}


static ssize_t second_read(struct file *filep,char __user *buf,size_t count,loff_t *ppos)
{
    int counter;
    counter=atomic_read(&second_devp->counter);
    if(put_user(counter,(int *)buf))
        return -EFAULT;
    else
    {
        return sizeof(unsigned int );
    }
}

static const struct file_operations second_fops={
    .owner=THIS_MODULE,
    .open=second_open,
    .release=second_release,
    .read=second_read,
};

static void second_setup_cdev(struct second_dev *dev,int index)
{
    int err;
    int devno=MKDEV(second_major,index);
    cdev_init(&dev->cdev,&second_fops);
    dev->cdev.owner=THIS_MODULE;
    err=cdev_add(&dev->cdev,devno,1);
    if(err)
    {
        printk(KERN_ERR "Failed to add second device\n");
    }
}


static int __init second_init(void)
{
    int ret;
    dev_t devno=MKDEV(second_major,0);
    if(second_major)
    {
        ret=register_chrdev_region(devno,1,"second");
    }
    else
    {
        ret=alloc_chrdev_region(&devno,0,1,"second");
        second_major=MAJOR(devno);
    }
    if(ret <0)
    {
        return ret;
    }
    second_devp=kzalloc(sizeof(*second_devp),GFP_KERNEL);
    if(!second_devp){
        ret=-ENOMEM;
        goto fail_malloc;
    }
    second_setup_cdev(second_devp,0);
    return 0;
fail_malloc:
    unregister_chrdev_region(devno,1);
    return ret;
    
}

module_init(second_init);

static void __exit second_exit(void)
{
    cdev_del(&second_devp->cdev);
    kfree(second_devp);
    unregister_chrdev_region(MKDEV(second_major,0),1);
}

module_exit(second_exit);

MODULE_AUTHOR("maple");
MODULE_LICENSE("GPL v2");

１second_dev结构中增加 timer_list的定时器结构．在调用 second_setup_cdev进行创建设备

２second_open中调用timer_setup进行定时器创建．在内核4.15以前使用的是init_timer．在4.15以后删除掉了init_timer．

其源码分析如下：

#define timer_setup(timer, callback, flags) \

__init_timer((timer), (callback), (flags))

原来这个是一个宏，其实还是调用的是__init_timer

#ifdef CONFIG_LOCKDEPz

#define __init_timer(_timer, _fn, _flags) \

do { \

static struct lock_class_key __key; \

init_timer_key((_timer), (_fn), (_flags), #_timer, &__key);\

} while (0)

#define __init_timer_on_stack(_timer, _fn, _flags) \

do { \

static struct lock_class_key __key; \

init_timer_on_stack_key((_timer), (_fn), (_flags), \

#_timer, &__key); \

} while (0)

#else

#define __init_timer(_timer, _fn, _flags) \

init_timer_key((_timer), (_fn), (_flags), NULL, NULL)

#define __init_timer_on_stack(_timer, _fn, _flags) \

init_timer_on_stack_key((_timer), (_fn), (_flags), NULL, NULL)

#endif

config_lockedp用于检测死锁，常用debug，这里假定没有开这个宏

所以这里的又会转调init_timer_key

void init_timer_key(struct timer_list *timer,

void (*func)(struct timer_list *), unsigned int flags,

const char *name, struct lock_class_key *key)

{

#如果没有打开CONFIG_DEBUG_OBJECTS_TIMERS的话，debug_init 为null

debug_init(timer);

#所以主要调用这个函数初始化timer

do_init_timer(timer, func, flags, name, key);

}

static void do_init_timer(struct timer_list *timer,

void (*func)(struct timer_list *),

unsigned int flags,

const char *name, struct lock_class_key *key)

{

#pprev 为null，说明这个timer处于pending状态，当然了刚开始创建timer的时候当然要pending了，毕竟

#还没有开始执行

timer->entry.pprev = NULL;

#时间到期要执行的回调函数

timer->function = func;

#看来flags中保存了当前的cpu id

timer->flags = flags | raw_smp_processor_id();

lockdep_init_map(&timer->lockdep_map, name, key, 0);

}

从上面的代码可以看到在timer_setup中已经将对timer的回调函数和参数做了一个初始化．在second_open中初始化了second_devp->counter以及定时器超时的参数

３　每当读取设备的时候的操作就是读取second_devp->counter值并放到用户空间．

makfile文件：

obj-m:=irq_test.o #产生irq_test模块的目标文件

#目标文件文件要与模块名字相同

CURRENT_PATH:=$(shell pwd) #模块所在的当前路径

LINUX_KERNEL:=$(shell uname -r) #linux内核代码的当前版本

LINUX_KERNEL_PATH:=/usr/src/linux-headers-$(LINUX_KERNEL)

CONFIG_MODULE_SIG=n

all:

make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) modules

clean:

make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) clean #清理模块

执行sudo insmod irq_test.ko报如下错误

insmod: ERROR: could not insert module irq_test.ko: Device or resource busy

执行cat /proc/devices　查看已存在的设备发现有deviceno=248的设备

Character devices:

1 mem

4 /dev/vc/0

4 tty

4 ttyS

5 /dev/tty

5 /dev/console

5 /dev/ptmx

5 ttyprintk

6 lp

7 vcs

10 misc

13 input

21 sg

29 fb

81 video4linux

89 i2c

99 ppdev

108 ppp

116 alsa

128 ptm

136 pts

180 usb

189 usb_device

204 ttyMAX

216 rfcomm

226 drm

241 media

242 aux

243 mei

244 hidraw

245 ttyDBC

246 bsg

247 hmm_device

248 watchdog

249 rtc

250 dax

251 dimmctl

252 ndctl

253 tpm

254 gpiochip

在代码中将SECOND_MAJOR修改成２６０. 编译后再插入就没问题了．

执行命令sudo mknod /dev/second c 260 0　创建一个设备

然后另外创建一个文件创建一个while循环不停的读/dev/second设备．这样就能不停的触发second_read获取econd_devp->counter的值

#include <stdio.h>

#include <sys/types.h>

#include <unistd.h>

#include <fcntl.h>

<br>int main()
{
    int fd;
    int counter=0;
    int old_counter=0;
    fd=open("/dev/second",O_RDONLY);
    if(fd != -1)
    {
        while(1)
        {
            read(fd,&counter,sizeof(unsigned int));
            if(counter != old_counter){
                printf("seconds after open /dev/second:%d\n",counter);
                old_counter=counter;
            }
        }
    }
    else{
        printf("open /dev/second failure\n");
    }
    return 1;
}

test@test:~/vs_code_prj$ ./test

seconds after open /dev/second:1

seconds after open /dev/second:2

seconds after open /dev/second:3

seconds after open /dev/second:4

seconds after open /dev/second:5

seconds after open /dev/second:6

seconds after open /dev/second:7

seconds after open /dev/second:8

seconds after open /dev/second:9

seconds after open /dev/second:10

seconds after open /dev/second:11

seconds after open /dev/second:12

seconds after open /dev/second:13

内核打印中也可以看到定时器定时的输出

[19294.462157] second_dev: loading out-of-tree module taints kernel.
[19294.462159] second_dev: module license 'GPL V2' taints kernel.
[19294.462160] Disabling lock debugging due to kernel taint
[19401.456462] current jiffies is 4299742872
[19402.480465] current jiffies is 4299743128
[19403.504256] current jiffies is 4299743384
[19404.528596] current jiffies is 4299743640
[19405.552647] current jiffies is 4299743896
[19406.577182] current jiffies is 4299744152
[19407.600567] current jiffies is 4299744408
[19408.624409] current jiffies is 4299744664
[19409.649629] current jiffies is 4299744920
[19410.673428] current jiffies is 4299745176
[19411.696759] current jiffies is 4299745432
[19412.721520] current jiffies is 4299745688
[19413.744562] current jiffies is 4299745944