IMX6ULL嵌入式Linux驱动学习
IMX6ULL－Linux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！
-
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_modules kernel_modules: $(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) modules clean: $(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) clean -
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，如果没有这个目录，可以自行创建。
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
-
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) -
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
-
linux内核使用
dev_ttypedef __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。 -
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_MMU
unsigned (*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
-
加载驱动
modprobe chrdevbase.ko -
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。 -
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");
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