第2课.字符设备驱动程序的开发

1.前言

Linux内核就是由各种驱动组成的
Linux操作系统将所有的设备都看成文件，以操作文件的方式访问设备。
应用程序不能直接操作硬件，而是通过使用统一的接口函数调用硬件驱动程序。

2.字符设备驱动程序中重要的数据结构和函数

重要的数据结构和函数

可以在glibc的fcntl.h、unistd.h、sys/ioctl.h等文件中看到（应用程序中使用的接口）

对于上述每个系统调用，驱动程序中国都有一个与之对应的函数对于字符设备驱动程序，这些函数集合在一个file_operations类型的数据结构中。file_operations结构在内核的include/linux/fs.h中定义

file_operations

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 (aio_read) (struct kiocb *, const struct iovec , unsigned long, loff_t);
ssize_t (aio_write) (struct kiocb *, const struct iovec , unsigned long, loff_t);
int (readdir) (struct file *, void , filldir_t);
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 (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 **);
long (fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
};
当应用程序使用open函数打开某个设备时，设备驱动程序的file_operations结构中的open成员函数会被调用。从这个角度来说，编写字符设备驱动程序就是为硬件的file_operations结构编写各个函数。

copy_from_user()和copy_to_user()

static inline unsigned long __must_check copy_from_user(void *to, const void __user *from, unsigned long n)
从用户空间得到数据
eg:
write传入的参数需要被copy_from_user从用户空间取出后才能使用
static inline unsigned long __must_check copy_to_user(void __user *to, const void *from, unsigned long n)
把数据传递给用户空间
eg：
同上read读取的参数，需要copy_to_user从内核中传出后才能read到

ioremap和iounmap

linux驱动直接操作不了内核，需要使用虚拟地址去映射，使用函数

static inline void __iomem *ioremap(phys_addr_t offset, unsigned long size)
phys_addr_t offset：物理地址
unsigned long size：虚拟地址

static inline void iounmap(void __iomem *addr)

module_init、module_exit和MODULE_LICENSE("GPL")

module_init、module_exit：指明驱动程序的初始化函数和卸载函数
MODULE_LICENSE("GPL")：遵循的协议

主次设备号

在PC上执行ls /dev/ttyS0 -l可以看到

crw-rw---- 1 root dialout 4, 64 3月 11 16:10 /dev/ttyS0
c表示/dev/ttyS0是一个字符设备。它的主设备号是4，次设备号是64。如果开头是b则为块设备

3.代码解析

Makefile

KERN_DIR = /work/system/linux-2.6.22.6
#KERN_DIR 内核的目录，需要先编译

all:
make -C $(KERN_DIR) M=pwd modules #该命令是make modules命令的扩展
#-C：进入KERN_DIR目录中去执行make
#pwd是让Makefile在构造modules目标之前返回到源代码目录，查找代码，并在其目录生成指定模块
clean:
make -C $(KERN_DIR) M=pwd modules clean
rm -rf modules.order # modules.order为编译时生成。用于记录模块在Makefile中出现的顺序。

obj-m += first_drv.o
#编译成模块
#make modules是单独编译模块，驱动被配置成M的都是modules，modules不会被编译进内核image，需要单独安装到rootfs。

first_drv.c

include <linux/module.h>

include <linux/kernel.h>

include <linux/fs.h>

include <linux/init.h>

include <linux/delay.h>

include <asm/uaccess.h>

include <asm/irq.h>

include <asm/io.h>

include <asm/arch/regs-gpio.h>

include <asm/hardware.h>

static struct class *firstdrv_class;
static struct class_device *firstdrv_class_dev;

volatile unsigned long *gpfcon = NULL;
volatile unsigned long *gpfdat = NULL;

static int first_drv_open(struct inode inode, struct file file)
{
//printk("first_drv_open\n");
/ 配置GPF4,5,6为输出 /
gpfcon &= ~((0x3<<(42)) | (0x3<<(52)) | (0x3<<(62)));
gpfcon |= ((0x1<<(42)) | (0x1<<(52)) | (0x1<<(62)));
return 0;
}

static ssize_t first_drv_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
int val;

//printk("first_drv_write\n");
//write传入的参数需要使用copy_from_user把其从用户空间中取到内核
copy_from_user(&val, buf, count); // copy_to_user();

if (val == 1)
{
// 点灯
*gpfdat &= ~((1<<4) | (1<<5) | (1<<6));
}
else
{
// 灭灯
*gpfdat |= (1<<4) | (1<<5) | (1<<6);
}

return 0;
}

static struct file_operations first_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 = first_drv_open,
.write = first_drv_write,
};

int major;
static int first_drv_init(void)
{
major = register_chrdev(0, "first_drv", &first_drv_fops); // 注册, 告诉内核

//创建设备文件
firstdrv_class = class_create(THIS_MODULE, "firstdrv");

firstdrv_class_dev = class_device_create(firstdrv_class, NULL, MKDEV(major, 0), NULL, "xyz"); /* /dev/xyz */

gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
gpfdat = gpfcon + 1;

return 0;
}

static void first_drv_exit(void)
{
unregister_chrdev(major, "first_drv"); // 卸载

class_device_unregister(firstdrv_class_dev);
class_destroy(firstdrv_class);
iounmap(gpfcon);
}

module_init(first_drv_init);
module_exit(first_drv_exit);

MODULE_LICENSE("GPL");

firstdrvtest.c

include <sys/types.h>

include <sys/stat.h>

include <fcntl.h>

include <stdio.h>

/* firstdrvtest on
* firstdrvtest off
*/
int main(int argc, char **argv)
{
int fd;
int val = 1;
fd = open("/dev/xyz", O_RDWR);
if (fd < 0)
{
printf("can't open!\n");
}
if (argc != 2)
{
printf("Usage :\n");
printf("%s <on|off>\n", argv[0]);
return 0;
}

if (strcmp(argv[1], "on") == 0)
{
val = 1;
}
else
{
val = 0;
}

write(fd, &val, 4);
return 0;
}