ldd3学习之十一(3)：Linux设备模型---platform总线分析

浅浅的花香味﹌ 2022-06-18 03:28 234阅读 0赞

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![Image 1][]**

**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.      struct device    dev;  
    
5.      u32        num\_resources;  
    
6.      struct resource    \* resource;//设备资源  
    
7.    
    
8.      struct platform\_device\_id    \*id\_entry;  
    
9.    
    
10.     /\* arch specific additions \*/  
    
11.     struct pdev\_archdata    archdata;  
    
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.  struct resource \{   
    
6.      resource\_size\_t start;//资源的起始物理地址  
    
7.      resource\_size\_t end;  //资源的结束物理地址  
    
8.      const char \*name;     //资源名称  
    
9.      unsigned long flags;  //资源类型，MEM,IO,IRQ  
    
10.     struct resource \*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.  static struct resource s3c\_wdt\_resource\[\] = \{   
    
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. struct platform\_device s3c\_device\_wdt = \{   
    
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.  struct resource \*platform\_get\_resource(struct platform\_device \*dev,  
    
8.                   unsigned 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.      void (\*shutdown)(struct platform\_device \*);  
    
5.      int (\*suspend)(struct platform\_device \*, pm\_message\_t state);  
    
6.      int (\*resume)(struct platform\_device \*);  
    
7.      struct device\_driver driver;  
    
8.      struct platform\_device\_id \*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.         .name    = "s3c2410-wdt",//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.  static int \_\_devinit s3c2410wdt\_probe(struct platform\_device \*pdev)  
    
4.  \{   
    
5.      struct resource \*res;  
    
6.      struct device \*dev;  
    
7.      unsigned int wtcon;  
    
8.      int started = 0;  
    
9.      int ret;  
    
10.     int size;  
    
11.   
    
12.     DBG("%s: probe=%p\\n", \_\_func\_\_, pdev);  
    
13.   
    
14.     dev = &pdev\->dev;  
    
15.     wdt\_dev = &pdev\->dev;  
    
16.   
    
17.     /\* get the memory region for the watchdog timer \*/  
    
18.   
    
19.     res = platform\_get\_resource(pdev, IORESOURCE\_MEM, 0);//获得资源，物理地址  
    
20.     if (res == NULL) \{   
    
21.         dev\_err(dev, "no memory resource specified\\n");  
    
22.         return \-ENOENT;  
    
23.     \}  
    
24.   
    
25.     size = (res\->end \- res\->start) \+ 1;  
    
26.     wdt\_mem = request\_mem\_region(res\->start, size, pdev\->name);  
    
27.     if (wdt\_mem == NULL) \{   
    
28.         dev\_err(dev, "failed to get memory region\\n");  
    
29.         ret = \-ENOENT;  
    
30.         goto err\_req;  
    
31.     \}  
    
32.   
    
33.     wdt\_base = ioremap(res\->start, size);  
    
34.     if (wdt\_base == NULL) \{   
    
35.         dev\_err(dev, "failed to ioremap() region\\n");  
    
36.         ret = \-EINVAL;  
    
37.         goto err\_req;  
    
38.     \}  
    
39.   
    
40.     DBG("probe: mapped wdt\_base=%p\\n", wdt\_base);  
    
41.   
    
42.     wdt\_irq = platform\_get\_resource(pdev, IORESOURCE\_IRQ, 0);//获得中断号  
    
43.     if (wdt\_irq == NULL) \{   
    
44.         dev\_err(dev, "no irq resource specified\\n");  
    
45.         ret = \-ENOENT;  
    
46.         goto err\_map;  
    
47.     \}  
    
48.   
    
49.     ret = request\_irq(wdt\_irq\->start, s3c2410wdt\_irq, 0, pdev\->name, pdev);//注册中断  
    
50.     if (ret != 0) \{   
    
51.         dev\_err(dev, "failed to install irq (%d)\\n", ret);  
    
52.         goto err\_map;  
    
53.     \}  
    
54.   
    
55.     wdt\_clock = clk\_get(&pdev\->dev, "watchdog");  
    
56.     if (IS\_ERR(wdt\_clock)) \{   
    
57.         dev\_err(dev, "failed to find watchdog clock source\\n");  
    
58.         ret = PTR\_ERR(wdt\_clock);  
    
59.         goto err\_irq;  
    
60.     \}  
    
61.   
    
62.     clk\_enable(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.         started = s3c2410wdt\_set\_heartbeat(  
    
69.                     CONFIG\_S3C2410\_WATCHDOG\_DEFAULT\_TIME);  
    
70.   
    
71.         if (started == 0)  
    
72.             dev\_info(dev,  
    
73.              "tmr\_margin value out of range, default %d used\\n",  
    
74.              CONFIG\_S3C2410\_WATCHDOG\_DEFAULT\_TIME);  
    
75.         else  
    
76.             dev\_info(dev, "default timer value is out of range, "  
    
77.                             "cannot start\\n");  
    
78.     \}  
    
79.   
    
80.     ret = misc\_register(&s3c2410wdt\_miscdev);  
    
81.     if (ret) \{   
    
82.         dev\_err(dev, "cannot register miscdev on minor=%d (%d)\\n",  
    
83.             WATCHDOG\_MINOR, ret);  
    
84.         goto err\_clk;  
    
85.     \}  
    
86.   
    
87.     if (tmr\_atboot && started == 0) \{   
    
88.         dev\_info(dev, "starting watchdog timer\\n");  
    
89.         s3c2410wdt\_start();  
    
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.         s3c2410wdt\_stop();  
    
96.     \}  
    
97.   
    
98.     /\* print out a statement of readiness \*/  
    
99.   
    
100.     wtcon = readl(wdt\_base \+ S3C2410\_WTCON);  
    
101.   
    
102.     dev\_info(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.     return 0;  
    
108.   
    
109.  err\_clk:  
    
110.     clk\_disable(wdt\_clock);  
    
111.     clk\_put(wdt\_clock);  
    
112.   
    
113.  err\_irq:  
    
114.     free\_irq(wdt\_irq\->start, pdev);  
    
115.   
    
116.  err\_map:  
    
117.     iounmap(wdt\_base);  
    
118.   
    
119.  err\_req:  
    
120.     release\_resource(wdt\_mem);  
    
121.     kfree(wdt\_mem);  
    
122.   
    
123.     return ret;  
    
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.      struct platform\_device \*pdev = to\_platform\_device(dev);  
    
4.      struct platform\_driver \*pdrv = to\_platform\_driver(drv);  
    
5.    
    
6.      /\* match against the id table first \*/  
    
7.      if (pdrv\->id\_table)  
    
8.          return platform\_match\_id(pdrv\->id\_table, pdev) != NULL;  
    
9.    
    
10.     /\* fall\-back to driver name match \*/  
    
11.     return (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：![Image 1][] platform.rar

实验结果：![Image 1][]

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