ldd3学习之十一(3)：Linux设备模型---platform总线分析

platform机制由两部分组成，platform_device和platform_driver。

Platform驱动与传统的设备驱动模型（即通过driver_register函数进行注册）相比，优势在于platform机制将设备本身的资源注册进内核，由内核统一管理，在驱动程序使用这些资源时使用统一的接口(即通过platform device提供的标准接口)，这样提高了程序可移植性。

platform 是一个虚拟的地址总线，相比 PCI、USB、I2C，它主要用于描述 SOC 上的片上资源。比如 S3C2410 上集成的控制器（ LCD、Watchdog、RTC等），platform 所描述的资源有一个共同点：在 CPU 的总线上直接取址。

用platform

1.平台设备

(1)描述

1. struct platform_device {
2. const char    * name;//设备名字
3. int        id;       //设备编号
4. ;
5. ;
6. * resource;//设备资源
7. 
   
8. *id_entry;
9. 
   
10. /* arch specific additions */
11. ;
12. };

(2)分配

1. struct platform_device *platform_device_alloc(const char *name, unsigned int id)
2. name:设备名
3. id：一般为-1

(3)注册

1. int platform_device_add(struct platform_device *pdev)
2. {
3. //增加的platform设备，都以platform_bus(platform设备)为父节点
4. if (!pdev->dev.parent) pdev->dev.parent = &platform_bus;
5. 
   
6. //platform类型设备都挂接在platform总线上 /sys/bus/platform/
7. pdev->dev.bus = &platform_bus_type;
8. .
9. .
10. .
11. }

(4)资源描述

1. /*
2. * Resources are tree-like, allowing
3. * nesting etc..
4. */
5. {
6. ;//资源的起始物理地址
7. end;  //资源的结束物理地址
8. const char *name;     //资源名称
9. ;  //资源类型，MEM,IO,IRQ
10. *parent, *sibling, *child; //资源链表指针
11. };

比如linux-2.6.32内核自带的s3c2410-wdt设备加载过程如下

1. /* Watchdog */
2. #define S3C24XX_VA_WATCHDOG S3C_VA_WATCHDOG
3. #define S3C2410_PA_WATCHDOG (0x53000000)
4. #define S3C24XX_SZ_WATCHDOG SZ_1M
5. 
   
6. #define S3C24XX_PA_WATCHDOG S3C2410_PA_WATCHDOG
7. 
   
8. [] = {
9. [0] = {//硬件寄存器资源
10. .start = S3C24XX_PA_WATCHDOG, //0x53000000
11. .end = S3C24XX_PA_WATCHDOG + S3C24XX_SZ_WATCHDOG - 1,
12. .flags = IORESOURCE_MEM,
13. },
14. [1] = {//中断资源
15. .start = IRQ_WDT,
16. .end = IRQ_WDT,
17. .flags = IORESOURCE_IRQ,
18. }
19. 
    
20. };
21. 
    
22. = {
23. .name         = "s3c2410-wdt",//name要与platform_driver中的name一致
24. .id         = -1,
25. .num_resources     = ARRAY_SIZE(s3c_wdt_resource),
26. .resource     = s3c_wdt_resource,
27. };
28. static struct platform_device *smdk2440_devices[] __initdata = {
29. &s3c_device_usb,
30. &s3c_device_lcd,
31. &s3c_device_wdt,//platform_device指针
32. &s3c_device_i2c0,
33. &s3c_device_iis,
34. };
35. static void __init smdk2440_machine_init(void)
36. {
37. s3c24xx_fb_set_platdata(&smdk2440_fb_info);
38. s3c_i2c0_set_platdata(NULL);

//添加所有platform设备

1. platform_add_devices(smdk2440_devices, ARRAY_SIZE(smdk2440_devices));
2. smdk_machine_init();
3. }
4. 
   
5. MACHINE_START(S3C2440, "SMDK2440")
6. /* Maintainer: Ben Dooks */
7. .phys_io = S3C2410_PA_UART,
8. .io_pg_offst = (((u32)S3C24XX_VA_UART) >> 18) & 0xfffc,
9. .boot_params = S3C2410_SDRAM_PA + 0x100,
10. 
    
11. .init_irq = s3c24xx_init_irq,
12. .map_io = smdk2440_map_io,
13. .init_machine = smdk2440_machine_init,
14. .timer = &s3c24xx_timer,
15. MACHINE_END
16. 
    
17. 
    

(5)获取资源方法

1. /**
2. * platform_get_resource - get a resource for a device
3. * @dev: platform device
4. * @type: resource type
5. * @num: resource index
6. */
7. *platform_get_resource(struct platform_device *dev,
8. int type, unsigned int num)
9. dev:资源所属设备
10. type:获取资源类型
11. num:获取的资源index
12. 比如：
13. platform_get_resource（pdev,IORESOURCE_IRQ,0）//获取中断号
14. platform_get_resource（pdev,IORESOURCE_MEM,0）//获取第0个资源

2.平台驱动

(1)描述

1. struct platform_driver {
2. int (*probe)(struct platform_device *);
3. int (*remove)(struct platform_device *);
4. (*shutdown)(struct platform_device *);
5. int (*suspend)(struct platform_device *, pm_message_t state);
6. int (*resume)(struct platform_device *);
7. ;
8. *id_table;
9. };

(2)注册

1. /**
2. * platform_driver_register
3. * @drv: platform driver structure
4. */
5. int platform_driver_register(struct platform_driver *drv)

在2.6.32内核s3c2410_wdt.c中实例注册过程

1. 
   
2. static struct platform_driver s3c2410wdt_driver = {
3. .probe        = s3c2410wdt_probe,
4. .remove        = __devexit_p(s3c2410wdt_remove),
5. .shutdown    = s3c2410wdt_shutdown,
6. .suspend    = s3c2410wdt_suspend,
7. .resume        = s3c2410wdt_resume,
8. .driver        = {
9. .owner    = THIS_MODULE,
10. //名字与platform_device中的name一致
11. },
12. };
13. static int __init watchdog_init(void)
14. {
15. printk(banner);
16. return platform_driver_register(&s3c2410wdt_driver);
17. }
18. 
    
19. static void __exit watchdog_exit(void)
20. {
21. platform_driver_unregister(&s3c2410wdt_driver);
22. }
23. module_init(watchdog_init);
24. module_exit(watchdog_exit);

(3)probe函数

执行时机：当所加载驱动与相应设备匹配成功

功能：获得设备资源，完成一个设备驱动所有的操作接口

(4)remove函数

执行：设备或驱动移除时

功能：释放probe申请的一切资源

比如s3c2410_wdt.c
1. /* device interface */
2. 
3. int __devinit s3c2410wdt_probe(struct platform_device *pdev)
4. {
5. *res;
6. *dev;
7. int wtcon;
8. int started = 0;
9. int ret;
10. int size;
11. 
12. ("%s: probe=%p\n", __func__, pdev);
13. 
14. = &pdev->dev;
15. = &pdev->dev;
16. 
17. /* get the memory region for the watchdog timer */
18. 
19. = platform_get_resource(pdev, IORESOURCE_MEM, 0);//获得资源，物理地址
20. if (res == NULL) {
21. (dev, "no memory resource specified\n");
22. -ENOENT;
23. }
24. 
25. = (res->end - res->start) + 1;
26. = request_mem_region(res->start, size, pdev->name);
27. if (wdt_mem == NULL) {
28. (dev, "failed to get memory region\n");
29. = -ENOENT;
30. ;
31. }
32. 
33. = ioremap(res->start, size);
34. if (wdt_base == NULL) {
35. (dev, "failed to ioremap() region\n");
36. = -EINVAL;
37. ;
38. }
39. 
40. ("probe: mapped wdt_base=%p\n", wdt_base);
41. 
42. = platform_get_resource(pdev, IORESOURCE_IRQ, 0);//获得中断号
43. if (wdt_irq == NULL) {
44. (dev, "no irq resource specified\n");
45. = -ENOENT;
46. ;
47. }
48. 
49. = request_irq(wdt_irq->start, s3c2410wdt_irq, 0, pdev->name, pdev);//注册中断
50. if (ret != 0) {
51. (dev, "failed to install irq (%d)\n", ret);
52. ;
53. }
54. 
55. = clk_get(&pdev->dev, "watchdog");
56. if (IS_ERR(wdt_clock)) {
57. (dev, "failed to find watchdog clock source\n");
58. = PTR_ERR(wdt_clock);
59. ;
60. }
61. 
62. (wdt_clock);
63. 
64. /* see if we can actually set the requested timer margin, and if
65. * not, try the default value */
66. 
67. if (s3c2410wdt_set_heartbeat(tmr_margin)) {
68. = s3c2410wdt_set_heartbeat(
69. );
70. 
71. if (started == 0)
72. (dev,
73. "tmr_margin value out of range, default %d used\n",
74. );
75. else
76. (dev, "default timer value is out of range, "
77. "cannot start\n");
78. }
79. 
80. = misc_register(&s3c2410wdt_miscdev);
81. if (ret) {
82. (dev, "cannot register miscdev on minor=%d (%d)\n",
83. , ret);
84. ;
85. }
86. 
87. if (tmr_atboot && started == 0) {
88. (dev, "starting watchdog timer\n");
89. ();
90. } else if (!tmr_atboot) {
91. /* if we're not enabling the watchdog, then ensure it is
92. * disabled if it has been left running from the bootloader
93. * or other source */
94. 
95. ();
96. }
97. 
98. /* print out a statement of readiness */
99. 
100. = readl(wdt_base + S3C2410_WTCON);
101. 
102. (dev, "watchdog %sactive, reset %sabled, irq %sabled\n",
103. (wtcon & S3C2410_WTCON_ENABLE) ? "" : "in",
104. (wtcon & S3C2410_WTCON_RSTEN) ? "" : "dis",
105. (wtcon & S3C2410_WTCON_INTEN) ? "" : "en");
106. 
107. ;
108. 
109. :
110. (wdt_clock);
111. (wdt_clock);
112. 
113. :
114. (wdt_irq->start, pdev);
115. 
116. :
117. (wdt_base);
118. 
119. :
120. (wdt_mem);
121. (wdt_mem);
122. 
123. ;
124. }

3.平台总线

(1)描述

1. struct bus_type platform_bus_type = {
2. .name        = "platform",
3. .dev_attrs    = platform_dev_attrs,
4. .match        = platform_match,
5. .uevent        = platform_uevent,
6. .pm        = &platform_dev_pm_ops,
7. };

(2)match方法:当platform总线上有设备或驱动变化时执行一次或多次

1. static int platform_match(struct device *dev, struct device_driver *drv)
2. {
3. *pdev = to_platform_device(dev);
4. *pdrv = to_platform_driver(drv);
5. 
   
6. /* match against the id table first */
7. if (pdrv->id_table)
8. (pdrv->id_table, pdev) != NULL;
9. 
   
10. /* fall-back to driver name match */
11. (strcmp(pdev->name, drv->name) == 0); //比较name成员
12. }

4.小结：

(1)当platform总线上有设备或驱动加入时，platform总线的match方法被调用一次或多次，遍历所有设备，一旦name成员与driver匹配成功，调用driver的probe方法，移除时调用remove方法。

(2)platform总线只是提供了一个管理硬件资源与设备的机制，驱动接口真正的实现在probe()函数内完成。

一个简单的platform机制测试代码：​​ platform.rar ​​  

实验结果：​​​​