字符设备驱动-poll机制
时间：2019-08-26 16:00:02
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[导读]
先来看三种按键驱动方式:
1、查询方法：一直在查询，不断去查询是否有事件发生，整个过程都是占用CPU资源，非常消耗CPU资源。
2、中断方式：当有事件发生时，就去跳转到相应事件去处
1、查询方法：一直在查询，不断去查询是否有事件发生，整个过程都是占用CPU资源，非常消耗CPU资源。 2、中断方式：当有事件发生时，就去跳转到相应事件去处理，CPU占用时间少。 3、poll方式: 中断方式虽然占用CPU资源少，但是在应用程序上需要不断在死循环里面执行读取函数，应用程序不能去做其它事情。poll机制解决了这个问题，当有事件发生时，才去执行读read函数，按键事件没有按下时<如果规定了时间，超过时间后返回无按键信息>，去执行其它的处理函数。 poll机制分析 一、poll内核框架： 所有的系统调用，都可以基于它的名字前加上“sys_”前缀，这就是它在内核中对应的函数。比如系统调用open、read、write、poll，与之对应的内核函数为：sys_open、sys_read、sys_write、sys_poll。先来看三种按键驱动方式:
① sys_poll函数位于fs/Select.c文件中，代码如下：对于系统调用poll或select，它们对应的内核函数都是sys_poll。分析sys_poll，即可理解poll机制。
asmlinkage long sys_poll(struct pollfd __user *ufds, unsigned int nfds,
long timeout_msecs)
{
s64 timeout_jiffies;
if (timeout_msecs > 0) {
#if HZ > 1000
/* We can only overflow if HZ > 1000 */
if (timeout_msecs / 1000 > (s64)0x7fffffffffffffffULL / (s64)HZ)
timeout_jiffies = -1;
else
#endif
timeout_jiffies = msecs_to_jiffies(timeout_msecs);
} else {
/* Infinite (< 0) or no (0) timeout */
timeout_jiffies = timeout_msecs;
}
return do_sys_poll(ufds, nfds, &timeout_jiffies);
}int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds, s64 *timeout)
{
……
poll_initwait(&table);
……
fdcount = do_poll(nfds, head, &table, timeout);
……
}poll_initwait > init_poll_funcptr(&pwq->pt, __pollwait); > pt->qproc = qproc;
即table->pt->qproc = __pollwait，__pollwait将在驱动的poll函数里用到。
static int do_poll(unsigned int nfds, struct poll_list *list,
struct poll_wqueues *wait, s64 *timeout)
{
01 ……
02 for (;;) {
03 ……
04 if (do_pollfd(pfd, pt)) {
05 count++;
06 pt = NULL;
07 }
08 ……
09 if (count || !*timeout || signal_pending(current))
10 break;
11 count = wait->error;
12 if (count)
13 break;
14
15 if (*timeout < 0) {
16 /* Wait indefinitely */
17 __timeout = MAX_SCHEDULE_TIMEOUT;
18 } else if (unlikely(*timeout >= (s64)MAX_SCHEDULE_TIMEOUT-1)) {
19 /*
20 * Wait for longer than MAX_SCHEDULE_TIMEOUT. Do it in
21 * a loop
22 */
23 __timeout = MAX_SCHEDULE_TIMEOUT - 1;
24 *timeout -= __timeout;
25 } else {
26 __timeout = *timeout;
27 *timeout = 0;
28 }
29
30 __timeout = schedule_timeout(__timeout);
31 if (*timeout >= 0)
32 *timeout += __timeout;
33 }
34 __set_current_state(TASK_RUNNING);
35 return count;
36 }static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
{
……
if (file->f_op && file->f_op->poll)
mask = file->f_op->poll(file, pwait);
……
}static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
{
if (p && wait_address)
p->qproc(filp, wait_address, p);
}static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
poll_table *p)
{
struct poll_table_entry *entry = poll_get_entry(p);
if (!entry)
return;
get_file(filp);
entry->filp = filp;
entry->wait_address = wait_address;
init_waitqueue_entry(&entry->wait, current);
add_wait_queue(wait_address, &entry->wait);
}驱动程序：fourth_drv.c
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
static struct class *fourthdrv_class;
static struct class_device *fourthdrv_class_dev;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
/* 中断事件标志, 中断服务程序将它置1，s3c24xx_fourth_read将它清0 */
static volatile int ev_press = 0;
volatile unsigned long *gpfcon;
volatile unsigned long *gpfdat;
volatile unsigned long *gpgcon;
volatile unsigned long *gpgdat;
struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
/* 键值： 按下时，0x01、0x02、0x03 */
/* 键值： 松开时，0x81、0x82、0x83 */
static unsigned char key_val;
struct pin_desc pin_desc[3] = {
{S3C2410_GPF0,0X01},
{S3C2410_GPF2,0X02},
{S3C2410_GPG3,0X03},
};
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);
*gpfdat |= ((1<<4) | (1<<5) | (1<<6));
}
else
{
/* 按下 */
key_val = pindesc->key_val;
*gpfdat &= ~((1<<4) | (1<<5) | (1<<6));
}
ev_press = 1; /* 表示中断发生了 */
wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */
return IRQ_RETVAL(IRQ_HANDLED);
}
static int fourth_drv_open(struct inode *inode,struct file *file)
{
/* 配置GPF0,2、GPG3为中断引脚 */
request_irq(IRQ_EINT0, buttons_irq,IRQT_BOTHEDGE,"s2",&pin_desc[0]);
request_irq(IRQ_EINT2, buttons_irq,IRQT_BOTHEDGE,"s3",&pin_desc[1]);
request_irq(IRQ_EINT11,buttons_irq,IRQT_BOTHEDGE,"s4",&pin_desc[2]);
/* 配置GPF4、5、6为输入引脚 */
*gpfcon &= ~((0x3<<4*2) | (0x3<<5*2) | (0x3<<6*2));
*gpfcon |= ((1<<4*2) | (1<<5*2) | (1<<6*2));
return 0;
}
static ssize_t fourth_drv_read (struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
//看用户需要读取的空间，和这里的是否相同
if(count != 1)
return -EINVAL;
/* 如果无按键动作发生，则进行休眠状态 */
/* 如果ev_press等于0，休眠 */
wait_event_interruptible(button_waitq,ev_press);
/* 如果有按键动作发生，则返回按键的值 */
copy_to_user(buf,&key_val,1);
ev_press = 0;
return 1;
}
static int fourth_drv_close (struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT0, &pin_desc[0]);
free_irq(IRQ_EINT2, &pin_desc[1]);
free_irq(IRQ_EINT11, &pin_desc[2]);
return 0;
}
static unsigned int fourth_drv_poll(struct file *file, struct poll_table_struct *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait);
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
static struct file_operations fourth_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 = fourth_drv_open,
.read = fourth_drv_read,
.release = fourth_drv_close,
.poll = fourth_drv_poll
};
int major;
static int fourth_drv_init(void)
{
major = register_chrdev(0,"fourth_drv",&fourth_drv_fops);
fourthdrv_class = class_create(THIS_MODULE,"fourthdrv");
fourthdrv_class_dev = class_device_create(fourthdrv_class,NULL,MKDEV(major,0),NULL,"buttons");
gpfcon = (volatile unsigned long *)ioremap(0x56000050,16);
gpfdat = gpfcon + 1;
gpgcon = (volatile unsigned long *)ioremap(0x56000060,16);
gpgdat = gpgcon + 1;
return 0;
}
static int fourth_drv_exit(void)
{
unregister_chrdev(major,"fourth_drv");
class_device_unregister(fourthdrv_class_dev);
class_destroy(fourthdrv_class);
iounmap(gpfcon);
iounmap(gpgcon);
return 0;
}
module_init(fourth_drv_init);
module_exit(fourth_drv_exit);
MODULE_LICENSE("GPL");
驱动测试程序:fourthdrvtest.c
#include
#include
#include
#include
#include
/*
* fourthdrvtest
*/
int main(int argc, char **argv)
{
int fd;
unsigned char key_val;
struct pollfd fds[1];
int ret;
fd = open("/dev/buttons",O_RDWR);
if(fd < 0)
{
printf("can't open!n");
}
fds[0].fd = fd;
fds[0].events = POLLIN;
while(1)
{
ret = poll(fds,1,5000);
if(ret == 0)
{
printf("Time out!n");
}
else
{
read(fd,&key_val,1);
printf("key_val = 0x%xn",key_val);
}
}
return 0;
} Makefile
KERN_DIR = /work/system/linux-2.6.22.6
all:
make -C $(KERN_DIR) M=`pwd` modules
clean:
make -C $(KERN_DIR) M=`pwd` modules clean
rm -rf modules.order
obj-m += fourth_drv.o测试命令：
make
arm-linux-gcc -o fourthdrvtest fourthdrvtest.c
cp fourthdrvtest fourth_drv.ko /work/nfs_root/czg
insmod fourth_drv.ko
./fourthdrvtest &
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