linux驱动入门之自动分配主设备号/创建设备节点

以韦东山老师视频为基础，加入自己的实践

1.second_drv.c文件

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>

#include <linux/device.h>
//包含class_create, device_create, ......这些程序

#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm/io.h>

//2.6.39版本内核为此位置
//之前版本的内核位置可能为
//#include <asm/regs-gpio.h>
//#include <asm/hardware.h>

#include <mach/regs-gpio.h>
#include <mach/hardware.h>

//加入两个结构体，用来供内核自动创建主设备号
//主要就是在init和exit两个函数中加入了这两个结构体
static struct class *seconddrv_class;
static struct class_device	*seconddrv_class_dev;

volatile unsigned long *gpfcon;
volatile unsigned long *gpfdat;

static int second_drv_open(struct inode *inode, struct file *file)
{
/* 配置GPF1,4,2,0为输入引脚 */
*gpfcon &= ~((0x3<<(1*2)) | (0x3<<(4*2)) | (0x3<<(2*2)) | (0x3<<(0*2)));
return 0;
}

ssize_t second_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
/* 返回4个引脚的电平 */
unsigned char key_vals[4];
int regval;

if (size != sizeof(key_vals))
return -EINVAL;

/* 读GPF1,4,2,0 */
regval = *gpfdat;
key_vals[0] = (regval & (1<<1)) ? 1 : 0;
key_vals[1] = (regval & (1<<4)) ? 1 : 0;
key_vals[2] = (regval & (1<<2)) ? 1 : 0;
key_vals[3] = (regval & (1<<0)) ? 1 : 0;

copy_to_user(buf, key_vals, sizeof(key_vals));

return sizeof(key_vals);
}

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   	=   second_drv_open,
.read		=	second_drv_read,
};

int major;
static int second_drv_init(void)
{
major = register_chrdev(0, "second_drv", &sencod_drv_fops);

seconddrv_class = class_create(THIS_MODULE, "second_drv");

//2.6.39版本的内核，函数变化为
//class_device_create ======> device_create
seconddrv_class_dev = device_create(seconddrv_class, NULL, MKDEV(major, 0), NULL, "buttons");// /dev/buttons

//地址映射
gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
gpfdat = gpfcon + 1;//加的是一个unsigned long的长度，即4个字节，到了0x56000054

return 0;
}

static void second_drv_exit(void)
{
unregister_chrdev(major, "second_drv");

//2.6.39版本的内核，函数变化为
// class_device_unregister ======> device_unregister
device_unregister(seconddrv_class_dev);

class_destroy(seconddrv_class);
iounmap(gpfcon);
}

module_init(second_drv_init);
module_exit(second_drv_exit);
MODULE_LICENSE("GPL");

2.makefile

KERN_DIR = /home/stevenking/workspace/code/linux-2.6.39

all:
make -C $(KERN_DIR) M=`pwd` modules

clean:
make -C $(KERN_DIR) M=`pwd` modules clean
rm -rf modules.order

obj-m	+= second_drv.o

3.seconddrvtest.c测试程序

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

/* seconddrvtest
*/
int main(int argc, char **argv)
{
int fd;
unsigned char key_vals[4];
int cnt = 0;

fd = open("/dev/buttons", O_RDWR);
if (fd < 0)
{
printf("can't open!\n");
}

while (1)
{
read(fd, key_vals, sizeof(key_vals));
if (!key_vals[0] || !key_vals[1] || !key_vals[2] || !key_vals[3])
{
printf("%04d key pressed: %d %d %d %d\n", cnt++, key_vals[0], key_vals[1], key_vals[2], key_vals[3]);
}
}

return 0;
}