Char Device Driver - 1_Architecture

驅動程式框架:
User space 的 APP 透過 open, read, write, close, ioctl, llseek, fsync 等函數來對應 Kernel space 裡的 Device driver: open, read,  write, close, ioctl, llseek, fsync 。
以 LED 驅動程式為例，架構如下，
----------------------------------------APP:  open, write
----------------------------------------system call
----------------------------------------VFS
----------------------------------------Device Driver:  led_open,  led_write
----------------------------------------Hardware

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驅動程式流程:

1. 設計led_open, led_write 撰寫硬體操作驅動程式
2. 構造 file_operation 中各成員函數
3. 將 file_operation 結構成員註冊進 kernel, 使用 int register_chrdev(unsigned int major, const char *name, struct file_operations *fops), 其中參數 major 為主設備號, name 為設備名稱,
4. 操作結束後需釋放裝置, 使用  unregister_chrdev(unsigned int major, const char *name)

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重要結構(需再研究其他結構)

1. file_operation 結構定義於 <linux/fs.h>, 含有字元驅動程式各作業方法的函式指標
2. file 結構定義於 <linux/fs.h>, 代表已開啟檔案
3. inode 結構代表檔案系統的節點(位於磁碟上的檔案)

實作1: 第一個驅動程式，只在 console 列印資訊
=========================================================
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 int first_drv_open(struct inode *inode, struct file *file)
{
printk("first_drv_open\n");
return 0;
}

static ssize_t first_drv_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
printk("first_drv_write\n");
return 0;
}

static struct file_operations first_drv_fops = 
{
.owner = THIS_MODULE, /* 這是一個巨集，推向編譯模組時自動創建的__this_module變數 */
.open = first_drv_open,
.write = first_drv_write,
};

static int first_drv_init(void)
{
register_chrdev(111, "first_drv", &first_drv_fops); // 向kernel註冊
return 0;
}

static void first_drv_exit(void)
{
unregister_chrdev(111, "first_drv"); // 卸載
}

module_init(first_drv_init);
module_exit(first_drv_exit);

MODULE_LICENSE("GPL");

=========================================================
Makefile


KERN_DIR = /home/scyu/share/linux_source/kernel/linux-2.6.22.6

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

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

obj-m += first_drv.o

=========================================================

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/xxx", O_RDWR);
    if (fd < 0) printf("can't open!\n");
    write(fd, &val, 4);
    return 0;
}

=========================================================

實驗結果:

# ls

bin         lib         mnt         sbin        usr

dev         linuxrc     proc        sys

etc         lost+found  root        tmp

# cd mnt/nfs/

# ls

first_drv.ko  firstdrvtest

# cat /proc/devices

Character devices:

  1 mem

  2 pty

  3 ttyp

  4 /dev/vc/0

  4 tty

  4 ttyS

  5 /dev/tty

  5 /dev/console

  5 /dev/ptmx

  6 lp

  7 vcs

 10 misc

 13 input

 14 sound

 29 fb

 90 mtd

 99 ppdev

116 alsa

128 ptm

136 pts

180 usb

189 usb_device

204 s3c2410_serial

253 usb_endpoint

254 rtc

Block devices:

  1 ramdisk

  7 loop

  8 sd

 31 mtdblock

 65 sd

 66 sd

 67 sd

 68 sd

 69 sd

 70 sd

 71 sd

128 sd

129 sd

130 sd

131 sd

132 sd

133 sd

134 sd

135 sd

179 mmc

# insmod first_drv.ko

# cat /proc/devices

Character devices:

  1 mem

  2 pty

  3 ttyp

  4 /dev/vc/0

  4 tty

  4 ttyS

  5 /dev/tty

  5 /dev/console

  5 /dev/ptmx

  6 lp

  7 vcs

 10 misc

 13 input

 14 sound

 29 fb

 90 mtd

 99 ppdev

111 first_drv         <--- 看到載入的驅動

116 alsa

128 ptm

136 pts

180 usb

189 usb_device

204 s3c2410_serial

253 usb_endpoint

254 rtc

Block devices:

  1 ramdisk

  7 loop

  8 sd

 31 mtdblock

 65 sd

 66 sd

 67 sd

 68 sd

 69 sd

 70 sd

 71 sd

128 sd

129 sd

130 sd

131 sd

132 sd

133 sd

134 sd

135 sd

179 mmc

# ./firstdrvtest

can't open!                             <-- 找不到設備節點

# mknod /dev/xxx c 111 0     <-- 手動掛載設備節點, 指定 major number

# ./firstdrvtest

first_drv_open

first_drv_write

=========================================================

實作2: 第一個驅動程式，只在 console 列印資訊，加入自動創建設備節點

=========================================================

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;

static int first_drv_open(struct inode *inode, struct file *file)

{

printk("first_drv_open\n");

return 0;

}

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

{

printk("first_drv_write\n");

return 0;

}

static struct file_operations first_drv_fops = 

{

.owner = THIS_MODULE, /* 這是一個巨集，推向編譯模組時自動創建的__this_module變數*/

.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); // 向kernel註冊, major number 隨系統創建，成功返回 major number，失敗返回0

firstdrv_class = class_create(THIS_MODULE, "firstdrv_class");

    firstdrv_class_dev = class_device_create(firstdrv_class, NULL, MKDEV(major, 0), NULL, "xyz");   // 系統自動創建 /dev/xyz

return 0;

}

static void first_drv_exit(void)

{

unregister_chrdev(major, "first_drv"); // 卸載

    class_device_unregister(firstdrv_class_dev);

    class_destroy(firstdrv_class);

}

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");

    write(fd, &val, 4);

    return 0;

}

=========================================================

實驗結果:

Please press Enter to activate this console.

starting pid 772, tty '/dev/s3c2410_serial0': '/bin/sh'

#

# ls

bin         lib         mnt         sbin        usr

dev         linuxrc     proc        sys

etc         lost+found  root        tmp

# cd mnt/nfs/

# ls

first_drv.ko  firstdrvtest

# insmod first_drv.ko     <-- 系統自動創建 /dev/xyz

# ls -l /dev/xyz

crw-rw----    1 0        0        252,   0 Jan  1 00:01 /dev/xyz

# cat /proc/devices

Character devices:

  1 mem

  2 pty

  3 ttyp

  4 /dev/vc/0

  4 tty

  4 ttyS

  5 /dev/tty

  5 /dev/console

  5 /dev/ptmx

  6 lp

  7 vcs

 10 misc

 13 input

 14 sound

 29 fb

 90 mtd

 99 ppdev

116 alsa

128 ptm

136 pts

180 usb

189 usb_device

204 s3c2410_serial

252 first_drv

253 usb_endpoint

254 rtc

Block devices:

  1 ramdisk

  7 loop

  8 sd

 31 mtdblock

 65 sd

 66 sd

 67 sd

 68 sd

 69 sd

 70 sd

 71 sd

128 sd

129 sd

130 sd

131 sd

132 sd

133 sd

134 sd

135 sd

179 mmc

# cd /sys/

# ls

block     class     firmware  kernel    power

bus       devices   fs        module

# cd class

# ls

firstdrv_class  misc            rtc             tty

graphics        mmc_host        scsi_device     usb_endpoint

hwmon           mtd             scsi_disk       usb_host

i2c-adapter     net             scsi_host       vc

input           ppdev           sound           vtconsole

mem             printer         spi_master

# cd firstdrv_class/

# ls

xyz

# cd xyz

# ls

dev        subsystem  uevent

# cat dev

252:0

# cd /mnt/nfs/

# ls

first_drv.ko  firstdrvtest

# rmmod first_drv.ko

# ls -l /dev/xyz

ls: /dev/xyz: No such file or directory   <-- 系統自動卸載

# insmod first_drv.ko

# ls -l /dev/xyz

crw-rw----    1 0        0        252,   0 Jan  1 00:03 /dev/xyz

# ls

first_drv.ko  firstdrvtest

# ./firstdrvtest

first_drv_open

first_drv_write
=========================================================
參考資料:

1. 嵌入式Linux應用開發完全手冊
2. Linux Device Driver (3rd)
3. Linux Kernel Development (3rd)