总线设备驱动模型---platform篇

源自 http://blog.chinaunix.net/uid-27664726-id-3334981.html

linux从2.6起就加入了一套新的驱动管理和注册的机制platform平台总线，是一条虚拟的总线，设备用platform_device表示，驱动用platform_driver进行注册。于传统的bus/device/driver机制相比，platform由内核进行统一管理，在驱动中使用资源，提高了代码的安全性和可移植性。

下面来看看内核时怎么注册platform总线的过程

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 int __init platform_bus_init(void)
 {
     int error;

     early_platform_cleanup();

     error = device_register(&platform_bus);//注册了platform的设备
     if (error)
         return error;
     error = bus_register(&platform_bus_type);//注册了platform总线
     if (error)
         device_unregister(&platform_bus);
     return error;
 }

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 struct device platform_bus = {
     .init_name    = "platform",
 };

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 struct bus_type platform_bus_type = {
     .name        = "platform",
     .dev_attrs    = platform_dev_attrs,
     .match        = platform_match,
     .uevent        = platform_uevent,
     .pm        = &platform_dev_pm_ops,
 };

其过程和总线的注册过程差不多，驱动和设备匹配后，调用platform的match函数。由传统的机制，也不难总结出platform的开发流程为

1、定义一个platform_device，并注册

2、定义一个platform_driver，并注册

定义platform_device过程

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 struct platform_device *platform_device_alloc(const char *name, int id)
 {
     struct platform_object *pa;

     pa = kzalloc(sizeof(struct platform_object) + strlen(name), GFP_KERNEL);
     if (pa) {
         strcpy(pa->name, name);
         pa->pdev.name = pa->name;
         pa->pdev.id = id;
         device_initialize(&pa->pdev.dev);
         pa->pdev.dev.release = platform_device_release;
         arch_setup_pdev_archdata(&pa->pdev);
     }

     return pa ? &pa->pdev : NULL;
 }

下面首先来看看platform_device的注册过程

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 struct platform_device {
     const char    * name;                  //设备名
     int        id;                         //设备ID
     struct device    dev;
     u32        num_resources;              //设备使用的资源的数目
     struct resource    * resource;         //设备使用的资源

     const struct platform_device_id    *id_entry;

     /* MFD cell pointer */
     struct mfd_cell *mfd_cell;

     /* arch specific additions */
     struct pdev_archdata    archdata;
 };

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 struct resource {
     resource_size_t start;
     resource_size_t end;
     const char *name;
     unsigned long flags;
     struct resource *parent, *sibling, *child;
 };

在struct resource结构中我们通常只关心start、end和flags这3个字段，分别表示资源的开始值、结束值和类型，flags可以用内存资源，IO资源，中断资源等。

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 int platform_device_register(struct platform_device *pdev)
 {
     device_initialize(&pdev->dev);//dev初始化
     arch_setup_pdev_archdata(pdev);
     return platform_device_add(pdev);//加入到dev链表
 }

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 int platform_device_add(struct platform_device *pdev)
 {
     int i, ret = 0;

     if (!pdev)
         return -EINVAL;

     if (!pdev->dev.parent)
         pdev->dev.parent = &platform_bus;//父设备设置为platform_bus

     pdev->dev.bus = &platform_bus_type;//设备挂载在platforrm总线上

     if (pdev->id != -1)
         dev_set_name(&pdev->dev, "%s.%d", pdev->name, pdev->id);
     else
         dev_set_name(&pdev->dev, "%s", pdev->name);

     for (i = 0; i < pdev->num_resources; i++) {    //完成资源的初始化
         struct resource *p, *r = &pdev->resource[i];

         if (r->name == NULL)
             r->name = dev_name(&pdev->dev);

         p = r->parent;
         if (!p) {
             if (resource_type(r) == IORESOURCE_MEM)
                 p = &iomem_resource;
             else if (resource_type(r) == IORESOURCE_IO)
                 p = &ioport_resource;
         }

         if (p && insert_resource(p, r)) {
             printk(KERN_ERR
              "%s: failed to claim resource %d\n",
              dev_name(&pdev->dev), i);
             ret = -EBUSY;
             goto failed;
         }
     }

     pr_debug("Registering platform device '%s'. Parent at %s\n",
          dev_name(&pdev->dev), dev_name(pdev->dev.parent));

     ret = device_add(&pdev->dev);
     if (ret == 0)
         return ret;

  failed:
     while (--i >= 0) {
         struct resource *r = &pdev->resource[i];
         unsigned long type = resource_type(r);

         if (type == IORESOURCE_MEM || type == IORESOURCE_IO)
             release_resource(r);
     }

     return ret;
 }

其上最后也是调用device_add的，其主要是将device加入到bus总线中，并由device_attach完成设备与驱动之间的匹配，这个过程在设备一篇中已经有详细的分析过程中，再看看驱动的注册过程。

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 struct platform_driver {
     int (*probe)(struct platform_device *);
     int (*remove)(struct platform_device *);
     void (*shutdown)(struct platform_device *);
     int (*suspend)(struct platform_device *, pm_message_t state);
     int (*resume)(struct platform_device *);
     struct device_driver driver;
     const struct platform_device_id *id_table;
 };

可见，它包含了设备操作的功能函数，同时包含了device_driver结构。内核提供的platform_driver结构的注册为

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 int platform_driver_register(struct platform_driver *drv)
 {
     drv->driver.bus = &platform_bus_type;//注册到总线上，drv与dev匹配通过platform_bus_type注册的platform_match完成
     if (drv->probe)
         drv->driver.probe = platform_drv_probe;
     if (drv->remove)
         drv->driver.remove = platform_drv_remove;
     if (drv->shutdown)
         drv->driver.shutdown = platform_drv_shutdown;

     return driver_register(&drv->driver);
 }

其注册函数中比较重要的还是调用了driver_register，添加到platform总线链表，完成设备与驱动之间的匹配过程，其主要的过程在总线设备驱动模型的驱动篇已经有过分析。

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 int driver_register(struct device_driver *drv)
 {
     int ret;
     struct device_driver *other;

     BUG_ON(!drv->bus->p);

     if ((drv->bus->probe && drv->probe) ||
      (drv->bus->remove && drv->remove) ||
      (drv->bus->shutdown && drv->shutdown))
         printk(KERN_WARNING "Driver '%s' needs updating - please use "
             "bus_type methods\n", drv->name);

     other = driver_find(drv->name, drv->bus);
     if (other) {
         put_driver(other);
         printk(KERN_ERR "Error: Driver '%s' is already registered, "
             "aborting...\n", drv->name);
         return -EBUSY;
     }

     ret = bus_add_driver(drv);
     if (ret)
         return ret;
     ret = driver_add_groups(drv, drv->groups);
     if (ret)
         bus_remove_driver(drv);
     return ret;
 }

下面看看看驱动和设备的匹配过程，由以前可以看出，主要是调用bus的match函数来完成匹配。

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 static int platform_match(struct device *dev, struct device_driver *drv)
 {
     struct platform_device *pdev = to_platform_device(dev);
     struct platform_driver *pdrv = to_platform_driver(drv);

     /* Attempt an OF style match first */
     if (of_driver_match_device(dev, drv))
         return 1;

     /* Then try to match against the id table */
     if (pdrv->id_table)
         return platform_match_id(pdrv->id_table, pdev) != NULL;

     /* fall-back to driver name match */
     return (strcmp(pdev->name, drv->name) == 0);
 }

由上面可以看出，只需要比较dev的名字和drv的名字，如果是相同的话就匹配成功。

在platform的设备驱动的编写有两种方法：

1、在bsp版文件中实现定义，在文件中将platform_device被化为一个数组，最后通过platform_add_devices函数注册。对于2440来说位于arch\arm\mach-s3c2440\mach-smdk2440.c中定义

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 static struct platform_device *smdk2440_devices[] __initdata = {
     &s3c_device_usb,
     &s3c_device_lcd,
     &s3c_device_wdt,
     &s3c_device_i2c,
     &s3c_device_iis,
 };

如果我们要实现一个设备的添加，那么只需要加入一个struct platform_device的数组，然后只需要编写对应的platform_driver驱动程序就可以了。从这种方法可以看出，存在一个很明显的缺点，如果要改写驱动，就要重新的编译内核。

2、第二种方法只需要单独编写一个内核模块加载到内核中。

例子：

device文件：platform_dev.c

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 struct platform_device *my_led_dev;

 static int __init platform_dev_init(void)
 {
     int ret;

  //分配一个 platform_device结构体
     my_led_dev = platform_device_alloc("platform_led", -1);

     ret = platform_device_add(my_led_dev);//将自定义的设备添加到内核设备架构中

     if(ret)
         platform_device_put(my_led_dev);//销毁platform设备结构

     return ret;
 }

 static void __exit platform_dev_exit(void)
 {
     platform_device_unregister(my_led_dev);//注销platform_device
 }

 module_init(platform_dev_init);
 module_exit(platform_dev_exit);

 MODULE_AUTHOR("Sola");
 MODULE_LICENSE("GPL");

drv文件：platform_drv.c

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 static int s3c6410_led_open(struct inode *inode, struct file *file)
 {
    unsigned tmp;
           tmp = readl(S3C64XX_GPMCON);
      tmp = (tmp & ~(0xFFFF))|(0x1111U);
           writel(tmp, S3C64XX_GPMCON);

      return 0;
 }


 static int s3c6410_led_close(struct inode *inode, struct file *file)
 {

     return 0;
 }


 static int s3c6410_led_read(struct file *filp, char __user *buff, size_t count, loff_t *offp)
 {
      printk("#########read######\n");
      return count;
 }

 static int s3c6410_led_write (struct file *filp, const char __user *buf, size_t count,loff_t *f_pos)
 {
      char wbuf[10];
      unsigned tmp;

      copy_from_user(wbuf,buf,count);
   if(wbuf[0]==1)//1号灯亮
      switch(wbuf[1])
      {
          case 0: //off
              tmp = readl(S3C64XX_GPMDAT);
                            tmp |= (0x1U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          case 1: //on
              tmp = readl(S3C64XX_GPMDAT);
                            tmp &= ~(0x1U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          default :
              break;
      }

   if(wbuf[0]==2)//2号灯亮
      switch(wbuf[1])
      {
          case 0: //off
              tmp = readl(S3C64XX_GPMDAT);
                            tmp |= (0x2U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          case 1: //on
              tmp = readl(S3C64XX_GPMDAT);
                            tmp &= ~(0x2U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          default :
              break;
      }

   if(wbuf[0]==3)//3号灯亮
      switch(wbuf[1])
      {
          case 0: //off
              tmp = readl(S3C64XX_GPMDAT);
                            tmp |= (0x4U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          case 1: //on
              tmp = readl(S3C64XX_GPMDAT);
                            tmp &= ~(0x4U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          default :
              break;
      }

   if(wbuf[0]==4)//4号灯亮
      switch(wbuf[1])
      {
          case 0: //off
              tmp = readl(S3C64XX_GPMDAT);
                            tmp |= (0x8U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          case 1: //on
              tmp = readl(S3C64XX_GPMDAT);
                            tmp &= ~(0x8U);
                            writel(tmp, S3C64XX_GPMDAT);
              break;
          default :
              break;
      }
      return count;
 }


 static struct file_operations led_fops = {
     .owner = THIS_MODULE,
     .open = s3c6410_led_open,
     .release = s3c6410_led_close,
     .read = s3c6410_led_read,
  .write = s3c6410_led_write,
 };


 static int my_plat_probe(struct platform_device *dev)
 {
     int rc;
  printk("Test platform_led dev\n");
  //注册设备
  rc = register_chrdev(LED_MAJOR,"platform_led",&led_fops);
   if (rc <0)
      {
          printk ("register %s char dev error\n","led");
          return -1;
      }
      printk ("ok!\n");
      return 0;
 }

 static int my_plat_remove(struct platform_device *dev)
 {
     printk("my platfrom device has removed.\n");
     return 0;
 }

 struct platform_driver my_led_drv = {
     .probe = my_plat_probe,
     .remove = my_plat_remove,
     .driver = {
         .owner = THIS_MODULE,
         .name = "platform_led",
     },
 };

 static int __init platform_drv_init(void)
 {
     int ret;

     ret = platform_driver_register(&my_led_drv);

     return ret;
 }

 static void __exit platform_drv_exit(void)
 {
     platform_driver_unregister(&my_led_drv);
 }

 module_init(platform_drv_init);
 module_exit(platform_drv_exit);

 MODULE_LICENSE("GPL");