SPI子系统分析之三:驱动模块

内核版本:3.9.5

SPI核心层(平台无关)

SPI子系统初始化的第一步就是将SPI总线注册进内核,并且在/sys下创建一个spi_master的类,以后注册的从设备都将挂接在该总线下. 下列函数位于drivers/spi/spi.c中:

 static int __init spi_init(void)
 {
     int    status;

     buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);/*初始化缓存*/
     if (!buf) {
         status = -ENOMEM;
         goto err0;
     }

     status = bus_register(&spi_bus_type);/*注册spi总线,此步骤之后就会在/sys/bus目录下生成spi子目录*/
     if (status < )
         goto err1;

     status = class_register(&spi_master_class);/*注册spi类,此步骤之后就会在/sys/class目录下生成spi_master子目录*/
     if (status < )
         goto err2;
     return ;

 err2:
     bus_unregister(&spi_bus_type);
 err1:
     kfree(buf);
     buf = NULL;
 err0:
     return status;
 }

 /* board_info is normally registered in arch_initcall(),
  * but even essential drivers wait till later
  *
  * REVISIT only boardinfo really needs static linking. the rest (device and
  * driver registration) _could_ be dynamically linked (modular) ... costs
  * include needing to have boardinfo data structures be much more public.
  */
 postcore_initcall(spi_init);

我们来看spi_bus_type的定义:

 /*和电源管理相关的结构*/
 static const struct dev_pm_ops spi_pm = {
     .suspend = spi_pm_suspend,
     .resume = spi_pm_resume,
     .freeze = spi_pm_freeze,
     .thaw = spi_pm_thaw,
     .poweroff = spi_pm_poweroff,
     .restore = spi_pm_restore,
     SET_RUNTIME_PM_OPS(
         pm_generic_runtime_suspend,
         pm_generic_runtime_resume,
         pm_generic_runtime_idle
     )
 };

 struct bus_type spi_bus_type = {
     .name        = "spi",
     .dev_attrs    = spi_dev_attrs,
     .match        = spi_match_device,
     .uevent        = spi_uevent,
     .pm        = &spi_pm,/*和电源管理相关的一些函数的结构封装*/
 };

来看看spi_match_device函数都做了什么:

 /* 名词解释of: OpenFirmware
  * 调用层次spi_match_device-->of_driver_match_device-->of_match_device-->
  * of_match_node
  * 用于驱动程序检查platform_device是否在其支持列表里
  */
 static int spi_match_device(struct device *dev, struct device_driver *drv)
 {
     const struct spi_device    *spi = to_spi_device(dev);
     const struct spi_driver    *sdrv = to_spi_driver(drv);

     /* Attempt an OF style match */
     /* 不匹配返回0；匹配返回非0，指向struct of_device_id类型的指针
      * dev:需要查找的设备; drv:驱动程序结构体
      */
     if (of_driver_match_device(dev, drv))
         return ;

     /* Then try ACPI */
     if (acpi_driver_match_device(dev, drv))
         return ;

     /*在驱动查找设备ID,找到返回真,否则假*/
     if (sdrv->id_table)
         return !!spi_match_id(sdrv->id_table, spi);

     return strcmp(spi->modalias, drv->name) == ;/*比较设备别名和驱动名称,匹配返回真*/
 }

这个函数比我还单纯,没有啥看的,但是其透露出的消息是重要的.这关系到spi_device和spi_driver的终身幸福,她们能不能彼此走在一起.
到这里,我觉得已经不可避免的要牵扯出控制器和驱动的注册了,这部分是平台相关的,留待下一节再讲.