目录

1 引入

2 应用编程

3 驱动编程

4 代码

4.1 gpio_key_drv.c

4.2 button_test.c

1 引入

所谓阻塞，就是等待某件事情发生。比如调用 read 读取按键时，如果没有按键数据则 read 函数不会返回，它会让线程休眠等待。 
使用 poll 时，如果传入的超时时间不为 0，这种访问方法也是阻塞的。 
使用 poll 时，可以设置超时时间为 0，这样即使没有数据它也会立刻返回，这就是非阻塞方式。能不能让 read 函数既能工作于阻塞方式，也可以工作于非阻塞方式？可以！ 
APP 调用 open 函数时，传入 O_NONBLOCK，就表示要使用非阻塞方式；默认是阻塞方式。 
注意：对于普通文件、块设备文件，O_NONBLOCK 不起作用。 
注 意 ： 对 于 字 符 设 备 文 件 ， O_NONBLOCK 起 作 用 的 前 提 是 驱 动 程 序 针 O_NONBLOCK 做了处理。 
只能在 open 时表明 O_NONBLOCK 吗？在 open 之后，也可以通过 fcntl 修改为阻塞或非阻塞。 

2 应用编程

open 时设置： 

int  fd = open(“/dev/xxx”, O_RDWR | O_NONBLOCK);  /* 非阻塞方式 */ 
int  fd = open(“/dev/xxx”, O_RDWR );  /* 阻塞方式 */ 

open 之后设置： 

int flags = fcntl(fd, F_GETFL); 
fcntl(fd, F_SETFL, flags | O_NONBLOCK);  /* 非阻塞方式 */ 
fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);  /* 阻塞方式 */ 

 3 驱动编程

以 drv_read 为例： 

static ssize_t drv_read(struct file *fp, char __user *buf, size_t count, loff_t *ppo
s) 
｛   
if (queue_empty(&as->queue) && fp->f_flags & O_NONBLOCK) return -EAGAIN; wait_event_interruptible(apm_waitqueue, !queue_empty(&as->queue)); …… 
｝ 

从驱动代码也可以看出来，当 APP 打开某个驱动时，在内核中会有一个struct  file 结构体对应这个驱动，这个结构体中有 f_flags，就是打开文件时的标记位；可以设置 f_flasgs 的 O_NONBLOCK 位，表示非阻塞；也可以清除这个位表示阻塞。 
驱动程序要根据这个标记位决定事件未就绪时是休眠和还是立刻返回。 

4 代码

4.1 gpio_key_drv.c

#include 
#include #include 
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#include 
#include struct gpio_key{int gpio;struct gpio_desc *gpiod;int flag;int irq;
} ;static struct gpio_key *gpio_keys_100ask;/* 主设备号                                                                 */
static int major = 0;
static struct class *gpio_key_class;/* 环形缓冲区 */
#define BUF_LEN 128
static int g_keys[BUF_LEN];
static int r, w;struct fasync_struct *button_fasync;#define NEXT_POS(x) ((x+1) % BUF_LEN)static int is_key_buf_empty(void)
{return (r == w);
}static int is_key_buf_full(void)
{return (r == NEXT_POS(w));
}static void put_key(int key)
{if (!is_key_buf_full()){g_keys[w] = key;w = NEXT_POS(w);}
}static int get_key(void)
{int key = 0;if (!is_key_buf_empty()){key = g_keys[r];r = NEXT_POS(r);}return key;
}static DECLARE_WAIT_QUEUE_HEAD(gpio_key_wait);/* 实现对应的open/read/write等函数，填入file_operations结构体                   */
static ssize_t gpio_key_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{//printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);int err;int key;if (is_key_buf_empty() && (file->f_flags & O_NONBLOCK))return -EAGAIN;wait_event_interruptible(gpio_key_wait, !is_key_buf_empty());key = get_key();err = copy_to_user(buf, &key, 4);return 4;
}static unsigned int gpio_key_drv_poll(struct file *fp, poll_table * wait)
{printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);poll_wait(fp, &gpio_key_wait, wait);return is_key_buf_empty() ? 0 : POLLIN | POLLRDNORM;
}static int gpio_key_drv_fasync(int fd, struct file *file, int on)
{if (fasync_helper(fd, file, on, &button_fasync) >= 0)return 0;elsereturn -EIO;
}/* 定义自己的file_operations结构体                                              */
static struct file_operations gpio_key_drv = {.owner	 = THIS_MODULE,.read    = gpio_key_drv_read,.poll    = gpio_key_drv_poll,.fasync  = gpio_key_drv_fasync,
};static irqreturn_t gpio_key_isr(int irq, void *dev_id)
{struct gpio_key *gpio_key = dev_id;int val;int key;val = gpiod_get_value(gpio_key->gpiod);printk("key %d %d\n", gpio_key->gpio, val);key = (gpio_key->gpio << 8) | val;put_key(key);wake_up_interruptible(&gpio_key_wait);kill_fasync(&button_fasync, SIGIO, POLL_IN);return IRQ_HANDLED;
}/* 1. 从platform_device获得GPIO* 2. gpio=>irq* 3. request_irq*/
static int gpio_key_probe(struct platform_device *pdev)
{int err;struct device_node *node = pdev->dev.of_node;int count;int i;enum of_gpio_flags flag;printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);count = of_gpio_count(node);if (!count){printk("%s %s line %d, there isn't any gpio available\n", __FILE__, __FUNCTION__, __LINE__);return -1;}gpio_keys_100ask = kzalloc(sizeof(struct gpio_key) * count, GFP_KERNEL);for (i = 0; i < count; i++){gpio_keys_100ask[i].gpio = of_get_gpio_flags(node, i, &flag);if (gpio_keys_100ask[i].gpio < 0){printk("%s %s line %d, of_get_gpio_flags fail\n", __FILE__, __FUNCTION__, __LINE__);return -1;}gpio_keys_100ask[i].gpiod = gpio_to_desc(gpio_keys_100ask[i].gpio);gpio_keys_100ask[i].flag = flag & OF_GPIO_ACTIVE_LOW;gpio_keys_100ask[i].irq  = gpio_to_irq(gpio_keys_100ask[i].gpio);}for (i = 0; i < count; i++){err = request_irq(gpio_keys_100ask[i].irq, gpio_key_isr, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, "100ask_gpio_key", &gpio_keys_100ask[i]);}/* 注册file_operations 	*/major = register_chrdev(0, "100ask_gpio_key", &gpio_key_drv);  /* /dev/gpio_key */gpio_key_class = class_create(THIS_MODULE, "100ask_gpio_key_class");if (IS_ERR(gpio_key_class)) {printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);unregister_chrdev(major, "100ask_gpio_key");return PTR_ERR(gpio_key_class);}device_create(gpio_key_class, NULL, MKDEV(major, 0), NULL, "100ask_gpio_key"); /* /dev/100ask_gpio_key */return 0;}static int gpio_key_remove(struct platform_device *pdev)
{//int err;struct device_node *node = pdev->dev.of_node;int count;int i;device_destroy(gpio_key_class, MKDEV(major, 0));class_destroy(gpio_key_class);unregister_chrdev(major, "100ask_gpio_key");count = of_gpio_count(node);for (i = 0; i < count; i++){free_irq(gpio_keys_100ask[i].irq, &gpio_keys_100ask[i]);}kfree(gpio_keys_100ask);return 0;
}static const struct of_device_id ask100_keys[] = {{ .compatible = "100ask,gpio_key" },{ },
};/* 1. 定义platform_driver */
static struct platform_driver gpio_keys_driver = {.probe      = gpio_key_probe,.remove     = gpio_key_remove,.driver     = {.name   = "100ask_gpio_key",.of_match_table = ask100_keys,},
};/* 2. 在入口函数注册platform_driver */
static int __init gpio_key_init(void)
{int err;printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);err = platform_driver_register(&gpio_keys_driver); return err;
}/* 3. 有入口函数就应该有出口函数：卸载驱动程序时，就会去调用这个出口函数*     卸载platform_driver*/
static void __exit gpio_key_exit(void)
{printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);platform_driver_unregister(&gpio_keys_driver);
}/* 7. 其他完善：提供设备信息，自动创建设备节点                                     */module_init(gpio_key_init);
module_exit(gpio_key_exit);MODULE_LICENSE("GPL");

4.2 button_test.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include static int fd;/** ./button_test /dev/100ask_button0**/
int main(int argc, char **argv)
{int val;struct pollfd fds[1];int timeout_ms = 5000;int ret;int	flags;int i;/* 1. 判断参数 */if (argc != 2) {printf("Usage: %s \n", argv[0]);return -1;}/* 2. 打开文件 */fd = open(argv[1], O_RDWR | O_NONBLOCK);if (fd == -1){printf("can not open file %s\n", argv[1]);return -1;}for (i = 0; i < 10; i++) {if (read(fd, &val, 4) == 4)printf("get button: 0x%x\n", val);elseprintf("get button: -1\n");}flags = fcntl(fd, F_GETFL);fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);while (1){if (read(fd, &val, 4) == 4)printf("get button: 0x%x\n", val);elseprintf("while get button: -1\n");}close(fd);return 0;
}