Linux嵌入式学习（简单 platform 设备驱动的实现）

话不多说，直接开始吧…

工作环境：VMware14+Ubuntu18.04
内核版本：5.0.0-21

编辑device.c

#include <linux/module.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/ioport.h>


static struct resource memdev_resource[] =
{
	[0] ={
		.start = 0x114000a0,
		.end =  0x114000a0 + 0x4,
		.flags = IORESOURCE_MEM,
	},

	[1] ={
		.start = 0x139D0000,
		.end =  0x139D0000 + 0x14,
		.flags = IORESOURCE_MEM,
	}
};

 

static void memdev_release(struct device *dev)
{
	printk("memdev_release\n");
	return ;
}


static struct platform_device memdev_device=
{
    .name = "my_memdev",
    .id = -1,
    .dev.release = memdev_release,
    .num_resources = ARRAY_SIZE(memdev_resource),
    .resource = memdev_resource,
};

 

static int memdev_init(void)
{
	printk("memdev_init");
	return platform_device_register(&memdev_device);
}

 

static void memdev_exit(void)
{
	printk("memdev_exit");
	platform_device_unregister(&memdev_device);
	return;
}

 
MODULE_LICENSE("GPL");
module_init(memdev_init);
module_exit(memdev_exit);

编辑driver.c

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <asm/io.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <asm/switch_to.h>
#include <linux/uaccess.h>
#include <linux/slab.h>


#define MEMDEV_MAJOR 0  		//预设的主设备号
#define MEMDEV_NR_DEVS 1		//次设备数
#define MEMDEV_SIZE 4096		//分配的内存空间大小

#define CLASS_NAME "memdev"
#define DEVICE_NAME "memdev"
         
/*mem设备描述结构体*/
struct mem_dev                                     
{                                                        
  char *data;                      
  unsigned long size;    
  struct semaphore sem;     /* 定义信号量 */   
};

static dev_t devno;

static struct class* class_memdever;

static int mem_major = MEMDEV_MAJOR;/*主设备号*/

module_param(mem_major, int, S_IRUGO);

struct mem_dev *mem_devp; /*设备结构体指针*/

struct cdev cdev; 

int mem_open(struct inode *inode, struct file *filp)
{
	struct mem_dev *dev;
    /*获取次设备号*/
    int num = MINOR(inode->i_rdev);
    
    if (num >= MEMDEV_NR_DEVS) /*MEMDEV_NR_DEVS设备数*/
    	return -ENODEV;    /*尚未分配到具体设备*/
    	
    dev = &mem_devp[num];  
    /*将设备描述结构指针赋值给文件私有数据指针*/
    filp->private_data = dev;
    
    return 0; 
}

/*文件释放函数*/
int mem_release(struct inode *inode, struct file *filp)
{
	return 0;
}


/*读函数 ssize_t是有符号整型，在32位机器上等同与int，在64位机器上等同与long int*/
/*char __user从用户态的指针，往用户态传数据 size_t等同unsigned int loff_t等同long类型*/
static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)
{
  	unsigned long p =  *ppos; /*文件当前的访问位置*/
  	unsigned int count = size;/*请求传输的数据量*/
  	int ret = 0;
  	struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/

    /* 获取信号量 */
  	if (down_interruptible(&dev->sem))
    	return -ERESTARTSYS;    /* -ERESTARTSYS表示信号函数处理完毕后重新执行信号函数前的某个系统调用*/
            
  	/*判断读位置是否有效*/
  	if (p >= MEMDEV_SIZE)
    	return 0;
    	
  	if (count > MEMDEV_SIZE - p)
    	count = MEMDEV_SIZE - p;

  	/*读数据到用户空间 copy_to_user（void _user *to, const void *from, int n)从from来，到to去，复制n个位*/
  	if (copy_to_user(buf, (void*)(dev->data + p), count))
  	{
    	ret =  - EFAULT;/*指针地址无法存取*/
    	goto out;
  	}
  	
  	else
  	{
    	*ppos += count;
    	ret = count;
    	printk(KERN_INFO "read %d bytes(s) from %ld\n", count, p);
  	}
	
	out:
    	/* 释放信号量 */
    	up(&dev->sem);
  		return ret;
}

/*写函数*/
static ssize_t mem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)
{
  	unsigned long p =  *ppos;
  	unsigned int count = size;
  	int ret = 0;
 	
 	struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
 
 
	/* 获取信号量 */
	if (down_interruptible(&dev->sem))
   	return -ERESTARTSYS; 
   	
  	/*分析和获取有效的写长度*/
  	if (p >= MEMDEV_SIZE)
    	return 0;
    	
  	if (count > MEMDEV_SIZE - p)
    	count = MEMDEV_SIZE - p;
    
  	/*从用户空间写入数据 copy_from_user（void *to, const void _user *from, int n)*/
  	if (copy_from_user(dev->data + p, buf, count))
  	{
    	ret =  - EFAULT;
    	goto out;
  	}
  	
  	else
  	{
    	*ppos += count;
    	ret = count;
    	printk(KERN_INFO "written %d bytes(s) from %ld\n", count, p);
  	}
	out:
		/* 释放信号量 */
  		up(&dev->sem);
  		return ret;
}

/* seek文件定位函数  loff_t等同long类型 offset位移量：“+” 向文件尾移、“-”的向回移 whence移动的基准点： 0 文件头、1 当前位置、2 文件尾*/
static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
{ 
	loff_t newpos;

    switch(whence) 
    {
      	case 0: /* SEEK_SET */
        	newpos = offset;/*从文件头开始定位*/
        	break;

      	case 1: /* SEEK_CUR */
        	newpos = filp->f_pos + offset;/*从文件中间开始定位*/
        	break;

      	case 2: /* SEEK_END */
        	newpos = MEMDEV_SIZE -1 + offset;/*从文件尾开始定位，由于是从0开始，要减1*/
        	break;

      	default: /* can't happen */
        	return -EINVAL;/*EINVAL是参数值不正确*/
    }
    
    if ((newpos<0) || (newpos>MEMDEV_SIZE))
    	return -EINVAL;
    	
    filp->f_pos = newpos;/*返回当前文件位置*/
    return newpos;
}

 

static struct file_operations mem_fops=

{
  .owner 	= THIS_MODULE,/*owner是一个struct module *类型的结构体指针,通过THIS_MODULE宏来引用模块的struct module结构*/
  .llseek 	= mem_llseek,
  .read 	= mem_read,
  .write 	= mem_write,
  .open 	= mem_open,
  .release 	= mem_release,
};

 

static int mem_probe(struct platform_device *pdev)
{
	int result;
  	int i;

  	devno = MKDEV(mem_major, 0);/*将主设备号和次设备号转换成dev_t类型*/

  	/* 静态申请设备号*/
  	if (mem_major)
    	result = register_chrdev_region(devno, 1, "memdev");
  	else  /* 动态分配设备号 */
  	{
    	result = alloc_chrdev_region(&devno, 0, 1, "memdev");
    	mem_major = MAJOR(devno);
  	}  
  
  	if (result < 0)
    	return result;

  	/*初始化cdev结构*/
  	cdev_init(&cdev, &mem_fops);
  	cdev.owner = THIS_MODULE;
  	cdev.ops = &mem_fops;
  
  	/* 注册字符设备 */
  	cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);
   
  	/* 为设备描述结构分配内存 */
  	/*GFP_KERNEL优先权允许kmalloc函数在系统空闲内存低于水平线min_free_pages时延迟分配函数的返回。当空闲内存太少时，kmalloc函数会使当前进程进入睡眠，等待空闲页的出现。*/
  	mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
  	
  	if (!mem_devp)    /*申请失败*/
  	{
    	result =  - ENOMEM;/*核心内存不足*/
    	goto fail_malloc;
  	}
	
	//初始化内存
  	memset(mem_devp, 0, sizeof(struct mem_dev));
  
  	/*为设备分配内存*/
  	for (i=0; i < MEMDEV_NR_DEVS; i++) 
  	{
    	mem_devp[i].size = MEMDEV_SIZE;
        mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
        memset(mem_devp[i].data, 0, MEMDEV_SIZE);
        sema_init(&mem_devp[i].sem, 1); 	//初始化信号量
  	}
  	
    class_memdever = class_create(THIS_MODULE,CLASS_NAME);
	device_create(class_memdever,NULL,devno,NULL,DEVICE_NAME);
	
  	return 0;

  	fail_malloc: 
  		unregister_chrdev_region(devno, 1);
  		return result;
}
 

static int mem_remove(struct platform_device *pdev)
{
  	device_destroy(class_memdever, devno);
	class_destroy(class_memdever);
	
  	cdev_del(&cdev);   /*注销设备*/
  	kfree(mem_devp);     /*释放设备结构体内存*/
  	unregister_chrdev_region(MKDEV(mem_major, 0), 1); /*释放设备号*/
}
 

static struct platform_driver mem_driver=
{
    .driver.name = "my_memdev",
    .probe = mem_probe,
    .remove = mem_remove,
};


static int mem_init(void)
{
	printk("mem_init");
	return platform_driver_register(&mem_driver);
}

 
static void mem_exit(void)
{
	printk("mem_exit");
	platform_driver_unregister(&mem_driver);
	return;
}

 
MODULE_LICENSE("GPL");
module_init(mem_init);
module_exit(mem_exit);

编辑Makefile

                                                                                                                                                                                                                   
ifneq  ($(KERNELRELEASE),)
 
obj-m:=device.o driver.o
 
$(info "2nd")
 
else
 
KDIR := /lib/modules/$(shell uname -r)/build
 
#KDIR := /home/fs/linux/linux-3.14-fs4412
 
PWD:=$(shell pwd)
 
all:
 
    $(info "1st")
 
    make -C $(KDIR) M=$(PWD) modules
 
clean:
 
    rm -f *.ko *.o *.symvers *.mod.c *.mod.o *.order
 
endif

编辑app.c

#include <stdio.h>

int main()
{
	FILE *fp0 = NULL;
	char Buf[4096];
	
	/*初始化Buf*/
	strcpy(Buf,"Mem is char dev!");
	printf("BUF: %s\n",Buf);
	
	/*打开设备文件*/
	fp0 = fopen("/dev/memdev","r+");
	if (fp0 == NULL)
	{
		printf("Open Memdev Error!\n");
		return -1;
	}
	
	/*写入设备*/
	fwrite(Buf, sizeof(Buf), 1, fp0);
	
	/*重新定位文件位置（思考没有该指令，会有何后果)*/
	fseek(fp0,0,SEEK_SET);
	
	/*清除Buf*/
	strcpy(Buf,"Buf is NULL!");
	printf("BUF: %s\n",Buf);
	
	
	/*读出设备*/
	fread(Buf, sizeof(Buf), 1, fp0);
	
	/*检测结果*/
	printf("BUF: %s\n",Buf);
	
	return 0;	

}

编译、加载和测试

• 命令行输入make进行编译，可以看到生成了一个device.ko和一个driver.ko
  
• 输入lsmod查看模块
  
• 输入cat /proc/devices查看设备
  
• 依次输入insmod device.koinsmod driver.ko, 一般来说应该先注册设备后注册驱动
• 这时再输入cat /proc/devices查看设备，就会发现240memdev设备出现了
  
• 输入ls /dev查看设备文件,在/dev目录下生成了memdev文件夹
  
• 使用gcc编译app.c，然后执行
  
• 输入dmesg | tail查看系统信息，可以看到设备和驱动的加载信息
  
• 最后卸载驱动 rmmod driver.ko 、卸载设备 rmmod device.ko