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一.  简介

前面一篇文章实现了驱动针对应用层阻塞式访问设备时的处理。文章地址如下：

Linux下阻塞IO驱动实验实例一-CSDN博客

本文也是通过编写驱动代码，以实现应用程序阻塞式访问设备。这里实现一种可以被信号打断的进程。

这里也是使用 Linux内核提供的 "等待队列"的方法。

二.  Linux下阻塞IO驱动实验实例二

这里的实验是在 14_block_io工程代码的基础上，进行更改。

1.  所调用的 Linux内核函数

wait_event_interruptible(wq, condition)
void wake_up(wait_queue_head_t *q)

2. 驱动代码实现

打开 14_block_io工程，key_irq.c文件实现代码如下：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <linux/timer.h>
#include <linux/of_irq.h>
#include <linux/interrupt.h>
#include <linux/types.h>
#include <asm/atomic.h>
#include <linux/wait.h>
#include <linux/sched.h>#define   IRQ_NAME          "key_irq"
#define   IRQ_CNT           1
#define   KEY_NUM           1 
#define   KEY0_VALUE        0x01  //key0按键值
#define   INVAL_KEY_VALUE   0xFF  //无效的按键值/*key按键结构体 */
struct key_dev{int gpio_number;        //IO编号int interrupt_number;   //中断号unsigned char value;    //键值unsigned char name[50]; //按键名字irqreturn_t (*handler)(int, void*); //中断处理函数
};/*imx6ull_irq设备结构体 */
struct irq_dev{dev_t devid;  //主设备号+次设备号int major; //主设备号int minor; //次设备号struct cdev cdev;struct class* class;struct device* device;struct device_node * dev_node;//设备节点struct key_dev key[KEY_NUM];struct timer_list timer; //定时器atomic_t key_value;      //按键值atomic_t key_release;    //按键释放标志wait_queue_head_t wait_queue_head; //等待队列头
};struct irq_dev irq;/* 打开设备函数*/
static int irq_dev_open(struct inode *inode, struct file *filp)
{filp->private_data = &irq;return 0;
}ssize_t irq_dev_read(struct file * filp, char __user * buf, size_t count, loff_t * ppos)
{int ret = 0;struct irq_dev* dev = filp->private_data;unsigned char key_release = 0;unsigned char key_value = 0;/*等待事件*/wait_event_interruptible(dev->wait_queue_head, atomic_read(&dev->key_release)); //等待按键有效key_release = atomic_read(&dev->key_release);key_value = atomic_read(&dev->key_value);if(key_release) //判断按键是否释放{if(key_value&0x80){key_value &= ~(0x80); //去掉标志位ret = copy_to_user(buf, &key_value, sizeof(key_value));if(ret != 0){printk("copy_to_user failed!\n");goto invalid_key;}}key_release = 0;atomic_set(&dev->key_release, 0);}else{goto invalid_key;}return ret;invalid_key: return -EINVAL;
}/* 关闭设备函数 */
int irq_dev_close(struct inode * inode, struct file * filp)
{return 0;
}static const struct file_operations irq_fops = {.open = irq_dev_open,.owner = THIS_MODULE,.read = irq_dev_read,.release = irq_dev_close, 
};/*定时器处理函数：对按键进行消抖处理 */
void timer_handler(unsigned long data)
{int value = 0;struct irq_dev* dev = (struct irq_dev*)data;//读取按键值value = gpio_get_value(dev->key[0].gpio_number);if(value == 0) //按键按下{// printk("KEY0 Press!\n");atomic_set(&dev->key_value, dev->key[0].value);}else if(value == 1) //按键释放{// printk("KEY0 Release!\n");//按键值最高位置1，打上标志atomic_set(&dev->key_value, (0x80|dev->key[0].value));atomic_set(&dev->key_release, 1); //一次完整的按键标志}/*按键有效时，唤醒进入休眠状态的进程 */ if(atomic_read(&dev->key_release)) //完成一次按键过程{wake_up(&dev->wait_queue_head);} 
}/* 中断处理函数 */
static irqreturn_t key0_irq_handler(int irq, void *param)
{struct irq_dev* dev = param;dev->timer.data = (volatile unsigned long)param;//设置定时器超时时间，开启定时器mod_timer(&dev->timer, jiffies + msecs_to_jiffies(20)); //按键按下后延时20msreturn IRQ_HANDLED;
}/*按键初始化 */
static int key_io_init(struct irq_dev* dev)
{int ret = 0;int i = 0;int n = 0;/*1.获取设备节点 */dev->dev_node = of_find_node_by_path("/key");if(NULL == dev->dev_node){printk("find dev_node failed!\n");goto find_dev_node;}/*2.获取IO编号 */for(i=0; i< KEY_NUM; i++){   dev->key[i].gpio_number = of_get_named_gpio(dev->dev_node, "key-gpio", i);if(dev->key[i].gpio_number < 0){printk("get gpio number failed!\n");goto get_gpio_number;}}/*3.申请IO */for(i = 0; i< KEY_NUM; i++){memset(dev->key[i].name, 0, sizeof(dev->key[i].name));sprintf(dev->key[i].name, "KEY%d", i);ret = gpio_request(dev->key[i].gpio_number, dev->key[i].name);if(ret != 0){printk("gpio request fail!\n");goto gpio_request;}/* 将GPIO设置为输入*/gpio_direction_input(dev->key[i].gpio_number);/* 获取中断号*/dev->key[i].interrupt_number = gpio_to_irq(dev->key[i].gpio_number);if(!dev->key[i].interrupt_number){printk("irq_of_parse_and_map fail!\n");goto get_irq_number;}}dev->key[0].handler = key0_irq_handler;dev->key[0].value = KEY0_VALUE;/*申请中断 */for(i=0; i<KEY_NUM; i++){ret = request_irq(dev->key[i].interrupt_number, dev->key[i].handler, (IRQF_TRIGGER_RISING|IRQF_TRIGGER_FALLING), dev->key[i].name, dev);  printk("request_irq ret: %d\n", ret);if(ret != 0){printk("%d request interrupt fail!\n", i);goto irq_request;}                     }/*定时器初始化 */init_timer(&dev->timer);dev->timer.function = timer_handler;return 0;irq_request:
get_irq_number:for(i=0; i<KEY_NUM; i++){gpio_free(dev->key[i].gpio_number);}
gpio_request:for(n = 0; n<i; n++){gpio_free(dev->key[n].gpio_number);}
get_gpio_number:
find_dev_node:return ret;
}/*驱动入口函数 */
static int __init imx6ull_irq_init(void)
{int ret = 0;/*1. 注册/申请设备号 */irq.major = 0;  if(irq.major) //如果给出主设备号，则注册设备号{irq.devid = MKDEV(irq.major, 0);ret = register_chrdev_region(irq.devid, IRQ_CNT, IRQ_NAME);	}else //否则申请设备号{ret = alloc_chrdev_region(&irq.devid, 0, IRQ_CNT, IRQ_NAME);irq.major = MAJOR(irq.devid);irq.minor = MINOR(irq.devid);}if(ret < 0){printk("devid apply failed!\n");goto devid_failed;}printk("dev: major: %d minor: %d\n", irq.major,irq.minor);/*2. 设备初始化，添加设备*/irq.cdev.owner = THIS_MODULE;cdev_init(&irq.cdev, &irq_fops);ret = cdev_add(&irq.cdev, irq.devid, IRQ_CNT);if(ret < 0){printk("cdev_add failed!\n");goto cdev_init_failed;}/*3. 自动创建设备节点 */irq.class = class_create(THIS_MODULE, IRQ_NAME);if(IS_ERR(irq.class)){printk(KERN_ERR "class_create failed!\n");ret = PTR_ERR(irq.class);goto class_create_failed;}irq.device = device_create(irq.class, NULL, irq.devid, NULL, IRQ_NAME);if (IS_ERR(irq.device)) {printk(KERN_ERR "device_create failed!\n");ret = PTR_ERR(irq.device);goto device_create_failed;}/*4. 按键初始化*/ret = key_io_init(&irq);if(ret != 0){printk("key_io_init failed!\n");goto key_io_init_failed;}/*初始原子变量*/atomic_set(&irq.key_value, INVAL_KEY_VALUE);atomic_set(&irq.key_release, 0); /*初始化等待队列头 */init_waitqueue_head(&irq.wait_queue_head);return 0;key_io_init_failed:device_destroy(irq.class, irq.devid);
device_create_failed:class_destroy(irq.class);
class_create_failed:cdev_del(&irq.cdev);
cdev_init_failed: unregister_chrdev_region(irq.devid, IRQ_CNT);
devid_failed:return ret;
}/*驱动出口函数 */
static void __exit imx6ull_irq_exit(void)
{int i = 0;/*删除定时器 */del_timer(&irq.timer);/*释放中断 */for(i=0; i < KEY_NUM; i++){free_irq(irq.key[i].interrupt_number, &irq);}/*释放GPIO编号 */for(i=0; i < KEY_NUM; i++){gpio_free(irq.key[i].gpio_number);}/*2. 删除设备 */cdev_del(&irq.cdev);/*3. 注销设备号*/unregister_chrdev_region(irq.devid, IRQ_CNT);/*4. 销毁设备 & 类*/device_destroy(irq.class, irq.devid);class_destroy(irq.class);
}/*驱动入口与出口函数 */
module_init(imx6ull_irq_init);
module_exit(imx6ull_irq_exit);
MODULE_LICENSE("GPL"); //驱动 License
MODULE_AUTHOR("WeiYing"); //作者

三.  编译驱动

对驱动代码进行编译，将驱动代码编译成驱动模块：

wangtian@wangtian-virtual-machine:~/zhengdian_Linux/Linux_Drivers/14_block_io$ make
make -C /home/wangtian/zhengdian_Linux/linux/kernel/linux-imx-rel_imx_4.1.15_2.1.0_ga M=/home/wangtian/zhengdian_Linux/Linux_Drivers/14_block_io modules
make[1]: 进入目录“/home/wangtian/zhengdian_Linux/linux/kernel/linux-imx-rel_imx_4.1.15_2.1.0_ga”CC [M]  /home/wangtian/zhengdian_Linux/Linux_Drivers/14_block_io/key_irq.oBuilding modules, stage 2.MODPOST 1 modulesCC      /home/wangtian/zhengdian_Linux/Linux_Drivers/14_block_io/key_irq.mod.oLD [M]  /home/wangtian/zhengdian_Linux/Linux_Drivers/14_block_io/key_irq.ko
make[1]: 离开目录“/home/wangtian/zhengdian_Linux/linux/kernel/linux-imx-rel_imx_4.1.15_2.1.0_ga”
wangtian@wangtian-virtual-machine:~/zhengdian_Linux/Linux_Drivers/14_block_io$

可以看出，驱动模块正常编译通过。

接下来就是对驱动模块进行测试。测试按键功能是否正常，按键进程的CPU占用率是否为 0，按键进程是否可以被杀死（即被信号打断）。