arm 驱动基础：字符设备驱动程序之同步互斥阻塞
1.原子操作：
原子操作指的是在执行过程中不会被别的代码路径所中断的操作。
常用的原子操作函数举例：
crucial_code
// 定义初始化原子变量 atomic_t *v = ATOMIC_INIT(1); // 读取并返回原子变量的值 atomic_read(atomic_t *v); // 原子变量加1 atomic_int(atomic_t *v); // 原子变量减1 atomic_dec(atomic_t *v); //原子变量减1并测试其值是否为0 ， 若是则函数返回true, 否则返回 false int atomic_dec_and_test(*v);
2.信号量：
crucial_code
// 定义、初始化信号量 struct semaphore sem; void sema_init(struct semaphore *sem, int val); // 定义、初始化互斥锁 struct semaphore sem; void init_MUTEX(struct semaphore *sem); //定义初始化一条龙 static DECLARE_MUTEX(button_lock); // 获得信号量 void down(struct semaphore *sem); // 若获取不到将进程将疆死 int down_interruptible(struct semaphore *sem); //若获取不到将等待，可被中断或kill, 若返回值不是0 ， 说明它被中断了 int down_trylock(struct semaphore *sem); //获取不到将返回真值，立即返回
3.阻塞：
阻塞操作
是指在执行设备操作时若不能获得资源则挂起进程， 直到满足可操作的条件后再进行操作。
非阻塞操作
进程在不能进行设备操作时并不挂起，它或者放弃、或者不停地查询，直至可以进行操作为止。
crucial_code
// app open 默认为O_BLOCK fd = open("......", O_RDWR | O_NONBLOCK); //sleep(5); sleep() 函数的时间单位是秒， poll(fds, 1, timeout); timeout 的时间单位是微秒。 // drv open if(filp->f_flags & O_NONBLOCK) { if(down_trylock(&button_lock)) { return -EBUSY; } }else { down(&button_lock); } //drv read if(filp->f_flags & O_NONBLOCK) { // 如果没有按键按下的话就会立即返回 if(!ev_press) { return -EAGAIN; } }else {// 如果是阻塞操作,则进程休眠 wait_event_interruptible(button_wait_q, ev_press); }
驱动程序代码：
sixth_drv.c
#include <linux/module.h> #include <linux/kernel.h> #include <linux/fs.h> #include <linux/init.h> #include <linux/delay.h> #include <linux/irq.h> #include <asm/uaccess.h> #include <asm/irq.h> #include <asm/io.h> #include <asm/arch/regs-gpio.h> #include <asm/hardware.h> #include <linux/poll.h> static struct class *sixthdrv_class; static struct class_device *sixthdrv_class_dev; volatile unsigned long *gpfcon; volatile unsigned long *gpfdat; volatile unsigned long *gpgcon; volatile unsigned long *gpgdat; static DECLARE_WAIT_QUEUE_HEAD(button_waitq); /* 中断事件标志, 中断服务程序将它置1，sixth_drv_read将它清0 */ static volatile int ev_press = 0; static struct fasync_struct *button_async; struct pin_desc{ unsigned int pin; unsigned int key_val; }; /* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */ /* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */ static unsigned char key_val; struct pin_desc pins_desc[4] = { {S3C2410_GPF0, 0x01}, {S3C2410_GPF2, 0x02}, {S3C2410_GPG3, 0x03}, {S3C2410_GPG11, 0x04}, }; //static atomic_t canopen = ATOMIC_INIT(1); //定义原子变量并初始化为1 static DECLARE_MUTEX(button_lock); //定义互斥锁 /* * 确定按键值 */ static irqreturn_t buttons_irq(int irq, void *dev_id) { struct pin_desc * pindesc = (struct pin_desc *)dev_id; unsigned int pinval; pinval = s3c2410_gpio_getpin(pindesc->pin); if (pinval) { /* 松开 */ key_val = 0x80 | pindesc->key_val; } else { /* 按下 */ key_val = pindesc->key_val; } ev_press = 1; /* 表示中断发生了 */ wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */ kill_fasync (&button_async, SIGIO, POLL_IN); return IRQ_RETVAL(IRQ_HANDLED); } static int sixth_drv_open(struct inode *inode, struct file *file) { #if 0 if (!atomic_dec_and_test(&canopen)) { atomic_inc(&canopen); return -EBUSY; } #endif if (file->f_flags & O_NONBLOCK) { if (down_trylock(&button_lock)) return -EBUSY; } else { /* 获取信号量 */ down(&button_lock); } /* 配置GPF0,2为输入引脚 */ /* 配置GPG3,11为输入引脚 */ request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]); request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]); request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]); request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]); return 0; } ssize_t sixth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos) { if (size != 1) return -EINVAL; if (file->f_flags & O_NONBLOCK) { if (!ev_press) return -EAGAIN; } else { /* 如果没有按键动作, 休眠 */ wait_event_interruptible(button_waitq, ev_press); } /* 如果有按键动作, 返回键值 */ copy_to_user(buf, &key_val, 1); ev_press = 0; return 1; } int sixth_drv_close(struct inode *inode, struct file *file) { //atomic_inc(&canopen); free_irq(IRQ_EINT0, &pins_desc[0]); free_irq(IRQ_EINT2, &pins_desc[1]); free_irq(IRQ_EINT11, &pins_desc[2]); free_irq(IRQ_EINT19, &pins_desc[3]); up(&button_lock); return 0; } static unsigned sixth_drv_poll(struct file *file, poll_table *wait) { unsigned int mask = 0; poll_wait(file, &button_waitq, wait); // 不会立即休眠 if (ev_press) mask |= POLLIN | POLLRDNORM; return mask; } static int sixth_drv_fasync (int fd, struct file *filp, int on) { printk("driver: sixth_drv_fasync\n"); return fasync_helper (fd, filp, on, &button_async); } static struct file_operations sencod_drv_fops = { .owner = THIS_MODULE, /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */ .open = sixth_drv_open, .read = sixth_drv_read, .release = sixth_drv_close, .poll = sixth_drv_poll, .fasync = sixth_drv_fasync, }; int major; static int sixth_drv_init(void) { major = register_chrdev(0, "sixth_drv", &sencod_drv_fops); sixthdrv_class = class_create(THIS_MODULE, "sixth_drv"); sixthdrv_class_dev = class_device_create(sixthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */ gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16); gpfdat = gpfcon + 1; gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16); gpgdat = gpgcon + 1; return 0; } static void sixth_drv_exit(void) { unregister_chrdev(major, "sixth_drv"); class_device_unregister(sixthdrv_class_dev); class_destroy(sixthdrv_class); iounmap(gpfcon); iounmap(gpgcon); return 0; } module_init(sixth_drv_init); module_exit(sixth_drv_exit); MODULE_LICENSE("GPL");
应用程序代码：
sixdrvtest.c
#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <poll.h> #include <signal.h> #include <sys/types.h> #include <unistd.h> #include <fcntl.h> /* sixthdrvtest */ int fd; void my_signal_fun(int signum) { unsigned char key_val; read(fd, &key_val, 1); printf("key_val: 0x%x\n", key_val); } int main(int argc, char **argv) { unsigned char key_val; int ret; int Oflags; //signal(SIGIO, my_signal_fun); fd = open("/dev/buttons", O_RDWR | O_NONBLOCK); if (fd < 0) { printf("can't open!\n"); return -1; } //fcntl(fd, F_SETOWN, getpid()); //Oflags = fcntl(fd, F_GETFL); //fcntl(fd, F_SETFL, Oflags | FASYNC); while (1) { ret = read(fd, &key_val, 1); printf("key_val: 0x%x, ret = %d\n", key_val, ret); sleep(5); } return 0; }