IMX6ULL嵌入式Linux驱动学习笔记（二）

IMX6ULL嵌入式Linux驱动开发学习

以下内容是我在学习正点原子IMX6ULL开发板alpha中记录的笔记，部分摘录自正点原子IMX6ULL开发手册。

一、字符设备驱动

字符设备驱动的编写主要就是驱动对应的open、close、read、write函数。其实就是file_operations结构体的成员变量的实现。

二、驱动模块的加载与卸载

Linux驱动程序可以编译到kernel里面，也就是zImage，也可以编译为模块(.ko)。测试的时候只需要加载.ko模块就行。

• module_init(xxx_init); //注册模块加载函数
• module_exit(xxx_exit) //注册模块卸载函数

编写驱动的时候注意事项！

1. 编译驱动的时候需要用到linux内核源码！因此需要解压缩linux源码，编译linux内核源码。得到zImage和dtb。需要使用编译后得到的zImage和dtb启动系统。

   vscode中设置linux源码所在路径，.vscode/c_cpp_properties.json：

   {"configurations": [{"name": "Linux","includePath": ["${workspaceFolder}/**","/home/rabbit/linux/IMX6UL/linux_image/linux-imx-alientek/include", "/home/rabbit/linux/IMX6UL/linux_image/linux-imx-alientek/arch/arm/include", "/home/rabbit/linux/IMX6UL/linux_image/linux-imx-alientek/arch/arm/include/generated/"],"defines": [],"compilerPath": "/usr/bin/gcc","cStandard": "c11","cppStandard": "c++17","intelliSenseMode": "clang-x64"}],"version": 4
   }
   

   makefile内容

   # 内核路径
   KERNELDIR := /home/rabbit/linux/IMX6UL/linux_image/linux-imx-alientek# 当前路径
   CURRENT_PATH := $(shell pwd)# 目标文件
   obj-m := chrdevbase.o# 规则
   build : kernel_moduleskernel_modules:$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) modulesclean:$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) clean
   

2. 将编译出来的.ko文件放到根文件系统中。加载驱动会用到加载命令：insmod，modprobe。移除驱动使用命令：rmmod，查看加载的驱动模块命令：lsmod。

   • insmod：不会解决模块的依赖关系。
   • modprobe：可以处理模块的依赖关系。推荐使用，modprobe会到/lib/modules/内核版本下查找相应的驱动模块。

   对于一个新的模块使用modprode加载的时候需要先调用一下depmod命令来分析可载入模块的相依性。

三、字符设备的注册与注销

1. 我们需要向系统注册一个字符设备，使用函数（即将弃用）：

   static inline init register_chrdev(unsigned int major, const char *name, const struct file_operations *fops)
   

2. 卸载驱动的时候需要注销掉前面注册的字符设备，使用函数（即将弃用）：

   static inline void unregister_chrdev(unsigned int major, const char *name)
   

   • major：主设备号，linux下每个设备都有一个设备号，设备号分为主设备号和次设备号两个部分。传入0自动分配。
   • name：设备名字，指向一串字符串。
   • fops：结构体file_operations类型指针，指向设备的操作函数集合变量。

四、设备号

1. linux内核使用dev_t

   typedef __kernel_dev_t		dev_t;
   typedef __u32 __kernel_dev_t;
   typedef unsigned int __u32;
   

   其中 dev_t 是一个无符号32位整型数据，其中高12位为主设备号(0～4096，表示同一类设备，比如IIC设备)，低20位为次设备号。

2. 设备号的操作函数或宏

   从dev_t获取主设备号和次设备号，MAJOR(dev_t)，MINOR(dev_t)，也可以使用主设备号和次设备号构成dev_t，通过MKDE(major, minor)即可。

五、file_operations的具体实现

struct file_operations {struct module *owner;loff_t (*llseek) (struct file *, loff_t, int);ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);int (*iterate) (struct file *, struct dir_context *);unsigned int (*poll) (struct file *, struct poll_table_struct *);long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);long (*compat_ioctl) (struct file *, unsigned int, unsigned long);int (*mmap) (struct file *, struct vm_area_struct *);int (*mremap)(struct file *, struct vm_area_struct *);int (*open) (struct inode *, struct file *);int (*flush) (struct file *, fl_owner_t id);int (*release) (struct inode *, struct file *);int (*fsync) (struct file *, loff_t, loff_t, int datasync);int (*aio_fsync) (struct kiocb *, int datasync);int (*fasync) (int, struct file *, int);int (*lock) (struct file *, int, struct file_lock *);ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);int (*check_flags)(int);int (*flock) (struct file *, int, struct file_lock *);ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);int (*setlease)(struct file *, long, struct file_lock **, void **);long (*fallocate)(struct file *file, int mode, loff_t offset,loff_t len);void (*show_fdinfo)(struct seq_file *m, struct file *f);
#ifndef CONFIG_MMUunsigned (*mmap_capabilities)(struct file *);
#endif
};

六、字符设备驱动框架

多借鉴别人的驱动程序。

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/ide.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>#define CHRDEVBASE_NAME		"chrdevbase"	// 名字
#define CHRDEVBASE_CNT		1/* 设备结构体 */
struct chrdev 
{dev_t devid;			/* 设备号 */int major;				/* 主设备号 */int minor;struct cdev cdev;		/* 字符设备 */struct class *class;	/* 类 */struct device *device;	/* 设备节点 */struct device_node *nd;	/* 设备树节点 */
};struct chrdev chrdevbase;static int chrdevbase_open(struct inode *inode, struct file *filp)
{filp->private_data = &chrdevbase;printk("chrdevbase_open!");return 0;
}static int chrdevbase_close(struct inode *inode, struct file *filp)
{struct chrdev *dev = filp->private_data;printk("chrdevbase_close!");return 0;
}static ssize_t chrdevbase_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{struct chrdev *dev = filp->private_data;printk("chrdevbase_read!");return 0;
}static ssize_t chrdevbase_write(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
{struct chrdev *dev = filp->private_data;printk("chrdevbase_write!");return 0;
}static struct file_operations chrdevbase_fops = {.owner = THIS_MODULE,.open = chrdevbase_open,.release = chrdevbase_close,.read = chrdevbase_read,.write = chrdevbase_write,
};static int __init chrdevbase_init(void)
{int ret = 0;/* 1.注册字符设备 *//* 1.1 申请设备号 */chrdevbase.major = 0;	/* 设备号由内核分配 */if (chrdevbase.major){/* 定义了设备号 */chrdevbase.devid = MKDEV(chrdevbase.major,0);ret = register_chrdev_region(chrdevbase.devid, CHRDEVBASE_CNT, CHRDEVBASE_NAME);}else{/* 没有给定设备号,向内核申请*/ret = alloc_chrdev_region(&chrdevbase.devid, 0, CHRDEVBASE_CNT, CHRDEVBASE_NAME);}if (ret < 0){goto fail_devid;}/* 1.1 添加字符设备 */chrdevbase.cdev.owner = THIS_MODULE;cdev_init(&chrdevbase.cdev, &chrdevbase_fops);ret = cdev_add(&chrdevbase.cdev, chrdevbase.devid, CHRDEVBASE_CNT);if (ret < 0){goto fail_cdev;}/* 3.自动创建设备节点 *//* 3.1 创建类 */chrdevbase.class = class_create(THIS_MODULE, CHRDEVBASE_NAME);if (IS_ERR(chrdevbase.class)){ret = PTR_ERR(chrdevbase.class);goto fail_class;}/* 3.2创建设备节点 */chrdevbase.device = device_create(chrdevbase.class, NULL, chrdevbase.devid, NULL, CHRDEVBASE_NAME);if (IS_ERR(chrdevbase.device)){ret = PTR_ERR(chrdevbase.device);goto fail_device;}return 0;fail_findnd:device_destroy(chrdevbase.class, chrdevbase.devid);
fail_device:class_destroy(chrdevbase.class);
fail_class:cdev_del(&chrdevbase.cdev);
fail_cdev:unregister_chrdev_region(chrdevbase.devid, CHRDEVBASE_CNT);
fail_devid:return ret;
}static void __exit chrdevbase_exit(void)
{/* 摧毁设备节点 */device_destroy(chrdevbase.class, chrdevbase.devid);/* 摧毁类 */class_destroy(chrdevbase.class);/* 删除字符设备 */cdev_del(&chrdevbase.cdev);/* 释放设备号 */unregister_chrdev_region(chrdevbase.devid, CHRDEVBASE_CNT);
}/*** 模块入口与出口* */
module_init(chrdevbase_init);	// 入口函数
module_exit(chrdevbase_exit);	// 出口函数
MODULE_LICENSE("GPL");
MODULE_AUTHOR("XXXX");

七、编写应用程序

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>/*** ./chrdevbaseAPP <filename>* @param argc 应用程序参数个数* @param argv 保存的参数，字符串形式。* */
int main(int argc, char *argv[])
{int ret = 0;int fd = 0;char *filename;char readbuf[100];char writebuf[100];filename = argv[1];fd = open(filename, O_RDWR);if(fd < 0) {printf("can't open file %s\r\n",filename);return -1;}/* 读 */ret = read(fd, readbuf, 10);if (ret < 0){printf("read file %s failed\r\n", filename);}else{/* code */}/* 写 */ret = write(fd, writebuf, 50);if (ret < 0){printf("write file %s failed\r\n", filename);}/* 关闭 */ret = close(fd);if (ret < 0){printf("close file %s failed\r\n", filename);}return 0;
}

八、测试

1. 加载驱动

   modprobe chrdevbase.ko
   

2. 进入/dev查看设备文件，chrdevbase。但是由于没有创建设备节点/dev/chrdevbase并不会存在。这里使用mknod /dev/chardevbase c 100 0手动创建设备节点。

3. 测试

   ./chrdevbaseAPP /dev/chrdevbase

九、完善chrdevbase虚拟字符设备驱动程序

• 驱动给应用传递数据的时候需要用到copy_to_user(to, from, n)函数；
• 应用给驱动传递数据的时候需要用到copy_from_user(to, from, n)函数；

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/uaccess.h>#define CHRDEVBASE_MAJOR	100				// 主设备号，0自动分配
#define CHRDEVBASE_NAME		"chrdevbase"	// 名字static char readbuf[100];
static char writebuf[100];
static char kerneldata[] = {"kernel data!"};static int chrdevbase_open(struct inode *inode, struct file *filp)
{printk("chrdevbase_open!\r\n");return 0;
}static int chrdevbase_close(struct inode *inode, struct file *filp)
{printk("chrdevbase_close!\r\n");return 0;
}static ssize_t chrdevbase_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{int ret = 0;/* printk("chrdevbase_read!\r\n"); */ret = copy_to_user(buf, kerneldata, count);if (ret == 0){/* code */}else{/* code */}return 0;
}static ssize_t chrdevbase_write(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
{int ret = 0;/* printk("chrdevbase_write!\r\n"); */ret = copy_from_user(writebuf, buf, count);if (ret == 0){printk("kernel recevdata:%s\r\n",writebuf);}else{/* code */}return 0;
}static struct file_operations chrdevbase_fops = {.owner = THIS_MODULE,.open = chrdevbase_open,.release = chrdevbase_close,.read = chrdevbase_read,.write = chrdevbase_write,
};static int __init chrdevbase_init(void)
{int ret = 0;printk("chrdevbase_init\r\n");/* 注册字符设备 */ret = register_chrdev(CHRDEVBASE_MAJOR, CHRDEVBASE_NAME, &chrdevbase_fops);if (ret < 0){printk("chrdevbase_init failed\r\n");}return 0;
}static void __exit chrdevbase_exit(void)
{printk("chrdevbase_exit\r\n");unregister_chrdev(CHRDEVBASE_MAJOR, CHRDEVBASE_NAME);/* 注销字符设备 */
}/*** 模块入口与出口* */
module_init(chrdevbase_init);	// 入口函数
module_exit(chrdevbase_exit);	// 出口函数MODULE_LICENSE("GPL");