S5PV210（TQ210）学习笔记——按键驱动程序

经过前面的配置，S5PV210开发已经可以成功进入Linux控制台了，那么，有了这个环境就可以开始学习Linux驱动的编写和测试了。学习Linux设备驱动，通常是从字符设备驱动开始。由于linux驱动开发具有比较系统的体系结构，我很难在一篇文章中阐述其开发思路，为了简单起见，从本文开始，自行编写的驱动将直接附上代码，对开发过程中感触比较深的地方稍作陈述。

我写的第一个驱动程序是Led的，但是感觉没有必要发出来了，S5PV210（TQ210）的按键驱动程序源码，仅供参考：

#include

#include

#include

#include

#include

#include

#include

#include

#include  

#include

#include

static dev_t devno;

static struct cdev cdev;

static struct class* buttons_class;

static struct device* buttons_device;

static wait_queue_head_t button_waitq;

static volatile int pressed = 0;

static unsigned char key_val;

struct key_desc{

unsigned int  pin;

unsigned char value;

};

static struct key_desc key_descs[8] = {

[0] = {

.pin = S5PV210_GPH0(0),

.value = 0x00,

},

[1] = {

.pin = S5PV210_GPH0(1),

.value = 0x01,

},

[2] = {

.pin = S5PV210_GPH0(2),

.value = 0x02,

},

[3] = {

.pin = S5PV210_GPH0(3),

.value = 0x03,

},

[4] = {

.pin = S5PV210_GPH0(4),

.value = 0x04,

},

[5] = {

.pin = S5PV210_GPH0(5),

.value = 0x05,

},

[6] = {

.pin = S5PV210_GPH2(6),

.value = 0x06,

},

[7] = {

.pin = S5PV210_GPH2(7),

.value = 0x07,

},

};

static irqreturn_t buttons_irq(int irq, void *dev_id){

volatile struct key_desc *key = (volatile struct key_desc *)dev_id;

if(gpio_get_value(key->pin)){

key_val = key->value|0x80;

}

else{

key_val = key->value;

}

pressed = 1;

wake_up_interruptible(&button_waitq);

return IRQ_RETVAL(IRQ_HANDLED);

}

static int buttons_open(struct inode *inode, struct file *file){

int ret;

ret = request_irq(IRQ_EINT(0),   buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key1', &key_descs[0]);

if(ret)

return ret;

ret = request_irq(IRQ_EINT(1),   buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key2', &key_descs[1]);

if(ret)

return ret;

  ret = request_irq(IRQ_EINT(2),   buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key3', &key_descs[2]);

if(ret)

return ret;

  ret = request_irq(IRQ_EINT(3),   buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key4', &key_descs[3]);

if(ret)

return ret;

ret = request_irq(IRQ_EINT(4),   buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key5', &key_descs[4]);

if(ret)

return ret;

ret = request_irq(IRQ_EINT(5),   buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key6', &key_descs[5]);

if(ret)

return ret;

ret = request_irq(IRQ_EINT(22),  buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key7', &key_descs[6]);

if(ret)

return ret;

ret = request_irq(IRQ_EINT(23),  buttons_irq, IRQ_TYPE_EDGE_BOTH, 'key8', &key_descs[7]);

if(ret)

return ret;

return 0;

}

static ssize_t buttons_read(struct file * file, char __user *data, size_t count, loff_t *loff){

if(count != 1){

printk(KERN_ERR 'The driver can only give one key value once!n');

return -ENOMEM;

}

wait_event_interruptible(button_waitq, pressed);

pressed = 0;

if(copy_to_user(data, &key_val, 1)){

printk(KERN_ERR 'The driver can not copy the data to user area!n');

return -ENOMEM;

}

return 0;

}

static int buttons_close(struct inode *inode, struct file *file){

free_irq(IRQ_EINT(0),  &key_descs[0]);

free_irq(IRQ_EINT(1),  &key_descs[1]);

free_irq(IRQ_EINT(2),  &key_descs[2]);

free_irq(IRQ_EINT(3),  &key_descs[3]);

free_irq(IRQ_EINT(4),  &key_descs[4]);

free_irq(IRQ_EINT(5),  &key_descs[5]);

free_irq(IRQ_EINT(22), &key_descs[6]);

free_irq(IRQ_EINT(23), &key_descs[7]);

return 0;

}

struct file_operations buttons_ops = {

.open    = buttons_open,

.read    = buttons_read,

.release = buttons_close,

};

int buttons_init(void){

int ret;

cdev_init(&cdev, &buttons_ops);

cdev.owner = THIS_MODULE;

ret = alloc_chrdev_region(&devno, 0, 1, 'buttons');

if(ret){

printk(KERN_ERR 'alloc char device region faild!n');

return ret;

}

ret = cdev_add(&cdev, devno, 1);

if(ret){

printk(KERN_ERR 'add char device faild!n');

goto add_error;

}

buttons_class = class_create(THIS_MODULE, 'buttonsdrv');

if(IS_ERR(buttons_class)){

printk(KERN_ERR 'create class error!n');

goto class_error;

}

buttons_device = device_create(buttons_class, NULL, devno, NULL, 'buttons');

if(IS_ERR(buttons_device)){

printk(KERN_ERR 'create buttons device error!n');

goto device_error;

}

init_waitqueue_head(&button_waitq);

return 0;

device_error:

class_destroy(buttons_class);

class_error:

cdev_del(&cdev);

add_error:

unregister_chrdev_region(devno,1);

return -ENODEV;

}

void buttons_exit(void){

device_destroy(buttons_class, devno);

class_destroy(buttons_class);

cdev_del(&cdev);

unregister_chrdev_region(devno, 1);

}

module_init(buttons_init);

module_exit(buttons_exit);

MODULE_LICENSE('GPL');

测试程序代码：

#include

#include

int main(){

int fd = open('/dev/buttons', O_RDWR);

if(fd < 0){

printf('open error');;

return 0;

}

unsigned char key;

while(1){

read(fd, &key, 1);

printf('The key = %xn', key);

}

close(fd);

}

相比轮询方式的按键驱动程序，中断方式编写的按键驱动程序可以很大程度上节省CPU资源，因此，推荐使用中断方式。

但是，这种方式有个弊端，如果一直接收不到按键，程序就会永远阻塞在这里，幸运的是，linux内核提供了poll机制，可以设置延迟时间，如果在这个时间内受到按键消息则取得键值，反之则超时退出。使内核支持poll非常简单，为file_operations的poll成员提供poll处理函数即可。

使内核支持poll还需要以下几步：

添加poll头文件

编写poll处理函数：

static unsigned buttons_poll(struct file *file, poll_table *wait){

unsigned int mask = 0;

poll_wait(file, &button_waitq, wait);

if (pressed)

mask |= POLLIN | POLLRDNORM;

return mask;

}

将poll处理函数添加给file_operations：

.poll    = buttons_poll,

这样，驱动程序就支持poll机制了。下面是poll方式的测试程序：

#include

#include

#include

#include

#include

int main(int argc, char **argv){

int fd;

unsigned char key_val;

int ret;

struct pollfd fds[1];

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 outn');

}

else{

read(fd, &key_val, 1);

printf('key_val = 0x%xn', key_val);

}

}

return 0;

}

这样按键驱动程序就完成了。如果您在编写测试阶段发现了其他问题