Linux下面一個簡單的虛擬platform驅動

在Linux之中，約定如果設備不屬於任何的總線，則可以把它注冊為虛擬的platform設備。

下面就簡單來學習一下一個簡單的platform設備是怎麼創建出來的。

一般注冊platform驅動的步驟是：

1，platform_device_create注冊一個設備

2，platform_driver_create注冊一個驅動。

static struct platform_driver chrdev_platform_driver = {
.probe = chrdev_probe,
.remove = chrdev_remove,
.driver = {
.name = CHRDEV_NAME,
.owner = THIS_MODULE,
},
};

static struct platform_device chrdev_platform_device = {
.name = CHRDEV_NAME,
.id = 0,
.dev = {
}
};

platform_device和platform_driver的名字必須一致

然後在chrdev_probe中完成注冊一個字符設備。一般注冊字符設備的流程如下：

1，alloc_chrdev_region分配一個未使用的設備號

2，cdev_init和cdev_add使用（1）分配到的設備號添加一個字符設備

如果到這裡就結束了，我們就需要使用分配到的設備號手動去建立/dev下面的設備節點，，，

在這裡可以使用class_create和device_create讓udev deamon自動為我們創建設備節點

3，class_create(THIS_MODULE, "chrdev");

4，device_create(chrdev_class, NULL, chrdev_devno, NULL, "chrdev");

當使用insmod把模塊加載到系統之後，www.linuxidc.com 就會在/dev下面自動創建名為"chrdev"的設備節點，模塊名字應該盡量跟注冊驅動的名字一致，不然可能會遇到不可測的問題。

源文件：chrdev.c

1. #include <linux/module.h>
2. #include <linux/init.h>
3. #include <linux/platform_device.h>
4. #include <linux/cdev.h>
5. #include <linux/fs.h>
6. ////////////////////////////////////////////////////////////////////////////////
7. /*
8. * Yao.GUET
9. * http://blog.csdn.net/Yao_GUET
10. * a simple platform character driver
11. */
12. ////////////////////////////////////////////////////////////////////////////////
13. MODULE_LICENSE("Dual BSD/GPL");
14. ////////////////////////////////////////////////////////////////////////////////
15. static int chrdev_open(struct inode *inode, struct file *file) {
16. printk(KERN_ALERT "chrdev open!\n");
17. return 0;
18. }
20. static int chrdev_release(struct inode *inode, struct file *file) {
21. printk(KERN_ALERT "chrdev release!\n");
22. return 0;
23. }
25. static int chrdev_ioctl(struct inode *inode, struct file *file,
26. unsigned int cmd, unsigned long arg) {
27. printk(KERN_ALERT "chrdev release!\n");
28. return 0;
29. }
31. // Kernel interface
32. static struct file_operations chrdev_fops = {
33. .owner = THIS_MODULE,
34. .ioctl = chrdev_ioctl,
35. .open = chrdev_open,
36. .release = chrdev_release,
37. };
40. #define CHRDEV_NAME "chrdev"
41. // driver interface
42. static struct class *chrdev_class = NULL;
43. static struct device *chrdev_device = NULL;
44. static dev_t chrdev_devno;
45. static struct cdev chrdev_cdev;
47. static int chrdev_probe(struct platform_device *dev) {
48. int ret = 0, err = 0;
50. printk(KERN_ALERT "chrdev probe!\n");
52. // alloc character device number
53. ret = alloc_chrdev_region(&chrdev_devno, 0, 1, CHRDEV_NAME);
54. if (ret) {
55. printk(KERN_ALERT " alloc_chrdev_region failed!\n");
56. goto PROBE_ERR;
57. }
58. printk(KERN_ALERT " major:%d minor:%d\n", MAJOR(chrdev_devno), MINOR(chrdev_devno));
60. cdev_init(&chrdev_cdev, &chrdev_fops);
61. chrdev_cdev.owner = THIS_MODULE;
62. // add a character device
63. err = cdev_add(&chrdev_cdev, chrdev_devno, 1);
64. if (err) {
65. printk(KERN_ALERT " cdev_add failed!\n");
66. goto PROBE_ERR;
67. }
69. // create the device class
70. chrdev_class = class_create(THIS_MODULE, CHRDEV_NAME);
71. if (IS_ERR(chrdev_class)) {
72. printk(KERN_ALERT " class_create failed!\n");
73. goto PROBE_ERR;
74. }
76. // create the device node in /dev
77. chrdev_device = device_create(chrdev_class, NULL, chrdev_devno,
78. NULL, CHRDEV_NAME);
79. if (NULL == chrdev_device) {
80. printk(KERN_ALERT " device_create failed!\n");
81. goto PROBE_ERR;
82. }
84. printk(KERN_ALERT " chrdev probe ok!\n");
85. return 0;
87. PROBE_ERR:
88. if (err)
89. cdev_del(&chrdev_cdev);
90. if (ret)
91. unregister_chrdev_region(chrdev_devno, 1);
92. return -1;
93. }
95. static int chrdev_remove (struct platform_device *dev) {
96. printk(KERN_ALERT " chrdev remove!\n");
98. cdev_del(&chrdev_cdev);
99. unregister_chrdev_region(chrdev_devno, 1);
101. device_destroy(chrdev_class, chrdev_devno);
102. class_destroy(chrdev_class);
103. return 0;
104. }
106. // platform_device and platform_driver must has a same name!
107. // or it will not work normally
108. static struct platform_driver chrdev_platform_driver = {
109. .probe = chrdev_probe,
110. .remove = chrdev_remove,
111. .driver = {
112. .name = CHRDEV_NAME,
113. .owner = THIS_MODULE,
114. },
115. };
117. static struct platform_device chrdev_platform_device = {
118. .name = CHRDEV_NAME,
119. .id = 0,
120. .dev = {
121. }
122. };
125. static __init int chrdev_init(void) {
126. int ret = 0;
127. printk(KERN_ALERT "chrdev init!\n");
129. ret = platform_device_register(&chrdev_platform_device);
130. if (ret) {
131. printk(KERN_ALERT " platform_device_register failed!\n");
132. return ret;
133. }
135. ret = platform_driver_register(&chrdev_platform_driver);
136. if (ret) {
137. printk(KERN_ALERT " platform_driver_register failed!\n");
138. return ret;
139. }
140. printk(KERN_ALERT " chrdev_init ok!\n");
141. return ret;
142. }
144. static __exit void chrdev_exit(void) {
145. printk(KERN_ALERT "chrdev exit!\n");
146. platform_driver_unregister(&chrdev_platform_driver);
147. }
149. module_init(chrdev_init);
150. module_exit(chrdev_exit);