Smart210学习记录----beep linux字符设备驱动

今天搞定了beep linux字符设备驱动，心里还是很开心的，哈哈。。。但在完成的过程中却遇到了一个非常棘手的问题，花费了我大量的时间，，，，

还是把问题描述一下吧，好像这个问题很普遍的，网上许多解决方法，但是我还是没看懂，只能慢慢找，，，

我在insmod字符设备是，出现了一下提示信息

这里只列出主要部分：

Unable to handle kernel NULL pointer dereference at virtual address 00000000

pgd = c0004000

[00000000] *pgd=00000000

Internal error: Oops: 7 [#2]

Modules linked in: cirrus

CPU: 0

PC is at dequeue_task+0xc/0x78

LR is at deactivate_task+0x38/0x44

pc : [ <c0039c44>]    lr : [ <c003a02c>]    Not tainted

sp : c0205cc4  ip : c0205cd4  fp : c0205cd0

r10: 0000038d  r9 : 72b90480  r8 : c020719c

r7 : c0206998  r6 : 0000000a  r5 : c0204000  r4 : c0206998

r3 : 00000001  r2 : 00000000  r1 : 00000000  r0 : c0206998

Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  Segment kernel

Control: C000717F  Table: 33B84000  DAC: 0000001D

Process swapper (pid: 0, stack limit = 0xc0204190)

Stack: (0xc0205cc4 to 0xc0206000)

5cc0:          c0205ce4 c0205cd4 c003a02c c0039c48 0000038d c0205d20 c0205ce8

5ce0: c01d52c4 c003a004 c0205d84 c02069cc 01312d00 c0206b40 0005f5d6 c0204000

5d00: 0000000a c0205d24 c020719c 00000048 00000000 c0205d60 c0205d24 c01d5b24

在网上查询可知，这是因为驱动中出现了空指针，，，，可是作为一个初学者，看了好几篇解决办法，感觉像是对牛弹琴，，，还是不会，，只能在驱动中慢慢找，不过还是被我给找到了，O(∩_∩)O
一个解决办法的网址：http://mengren425.blog.163.com/blog/static/56903931201525502222/

以下是beep驱动程序：

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/ioctl.h>
#include <linux/cdev.h>
#include <linux/delay.h>
#include <linux/device.h>

#include <mach/gpio.h>
#include <mach/regs-gpio.h>
#include <plat/gpio-cfg.h>

#define BEEPNAME  "mybeep"
static int beepmajor = 0;

#define BEEPON    1
#define BEEPOFF   0

static struct class* my_beep_class;
static struct device* my_beep_device;

struct beep_device {
struct cdev beep_dev;
unsigned char value;
};

struct beep_device* beep_device;

static int my_beep_open(struct inode *node, struct file *filep)
{
gpio_request(S5PV210_GPD0(0),BEEPNAME);
s3c_gpio_cfgpin(S5PV210_GPD0(0), S3C_GPIO_OUTPUT);
gpio_set_value(S5PV210_GPD0(0), 0);
return 0;
}

static int my_beep_close(struct inode * inode,struct file * file)
{
return 0;
}

static long my_beep_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
{
switch(cmd) {
case BEEPON:
printk("beep on\n");
beep_device->value = 1;
gpio_set_value(S5PV210_GPD0(0), 1);
break;

case BEEPOFF:
printk("beep off\n");
beep_device->value = 0;
gpio_set_value(S5PV210_GPD0(0), 0);
break;

default:
return -EUNATCH;
}
return 0;
}

struct file_operations beep_ops = {
.owner  =  THIS_MODULE,
.unlocked_ioctl = my_beep_ioctl,
.open   =  my_beep_open,
.release = my_beep_close,
};

static void beep_setup_cdev(struct cdev *dev, int minor,struct file_operations *fops)
{
int err;
dev_t deno;
deno = MKDEV(beepmajor, minor);
cdev_init(&beep_device->beep_dev, &beep_ops);
beep_device->beep_dev.owner = THIS_MODULE;
beep_device->beep_dev.ops = &beep_ops;
err = cdev_add(&beep_device->beep_dev, deno, 1);
if(err) {
printk("beep cdev_add error");
}
}

static int __init mybeep_init(void)
{
dev_t deno;
deno = MKDEV(beepmajor, 0);

if(beepmajor) {
register_chrdev_region(deno, 1, BEEPNAME);
printk(KERN_EMERG"beep major is %d\n", beepmajor);
} else {
if (alloc_chrdev_region(&deno, 0, 1, BEEPNAME))
printk(KERN_EMERG"alloc_chrdev_region error\n");
beepmajor = MAJOR(deno);
printk("beep major is %d\n", beepmajor);
}

beep_device = kmalloc(sizeof(struct beep_device), GFP_KERNEL);
if(!beep_device) {
printk("beep kmalloc error\n");
}
memset(beep_device, 0, sizeof(struct beep_device));

beep_setup_cdev(&beep_device->beep_dev, 0, &beep_ops);

my_beep_class= class_create(THIS_MODULE, BEEPNAME);
if(IS_ERR(my_beep_class)) {
printk(KERN_EMERG"class_create error\n");
}

my_beep_device= device_create(my_beep_class, NULL, deno, NULL, "mybeep");
if(IS_ERR(my_beep_device)) {
printk(KERN_EMERG"device_create error\n");
}
return 0;
}

static void __exit mybeep_exit(void)
{
unregister_chrdev_region(MKDEV(beepmajor, 0), 1);
cdev_del(&beep_device->beep_dev);
device_unregister(my_beep_device);
class_destroy(my_beep_class);
}

MODULE_LICENSE("Dual BSD/GPL");
module_init(mybeep_init);
module_exit(mybeep_exit);

测试程序：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define BEEPON  1
#define BEEPOFF 0

int main(void)
{
int dev_fd;
int i ;
dev_fd = open("/dev/mybeep", O_RDWR | O_NONBLOCK);
if (dev_fd == -1) {
printf ("Can't open /dev/mybeep\n");
exit(1);
}

ioctl(dev_fd, BEEPON, 0);
for(i = 500000; i > 0; i ++);
ioctl(dev_fd, BEEPOFF, 0);
close(dev_fd);
return 0;
}