module_platform_driver源码分析
在Linux设备驱动开发使用platform平台驱动模型过程中，在定义且初始化好platform_driver结构体变量以后，我们需要向 Linux 内核注册一个platform 驱动，Linux kernel中有两种方法，源码：include/linux/platform_device.h
方式一：
/* * use a macro to avoid include chaining to get THIS_MODULE */ #define platform_driver_register(drv) \ __platform_driver_register(drv, THIS_MODULE) extern int __platform_driver_register(struct platform_driver *, struct module *); /** * __platform_driver_register - register a driver for platform-level devices * @drv: platform driver structure * @owner: owning module/driver */ int __platform_driver_register(struct platform_driver *drv, struct module *owner) { drv->driver.owner = owner; drv->driver.bus = &platform_bus_type; /* 最终调用driver_register来注册drv->driver */ return driver_register(&drv->driver); } EXPORT_SYMBOL_GPL(__platform_driver_register); /** * platform_driver_unregister - unregister a driver for platform-level devices * @drv: platform driver structure */ void platform_driver_unregister(struct platform_driver *drv) { driver_unregister(&drv->driver); } EXPORT_SYMBOL_GPL(platform_driver_unregister);
方式二：
/* module_platform_driver() - Helper macro for drivers that don't do * anything special in module init/exit. This eliminates a lot of * boilerplate. Each module may only use this macro once, and * calling it replaces module_init() and module_exit() */ #define module_platform_driver(__platform_driver) \ module_driver(__platform_driver, platform_driver_register, \ platform_driver_unregister) /** * module_driver() - Helper macro for drivers that don't do anything * special in module init/exit. This eliminates a lot of boilerplate. * Each module may only use this macro once, and calling it replaces * module_init() and module_exit(). * * @__driver: driver name * @__register: register function for this driver type * @__unregister: unregister function for this driver type * @...: Additional arguments to be passed to __register and __unregister. * * Use this macro to construct bus specific macros for registering * drivers, and do not use it on its own. */ #define module_driver(__driver, __register, __unregister, ...) \ static int __init __driver##_init(void) \ { \ return __register(&(__driver) , ##__VA_ARGS__); \ } \ module_init(__driver##_init); \ static void __exit __driver##_exit(void) \ { \ __unregister(&(__driver) , ##__VA_ARGS__); \ } \ module_exit(__driver##_exit); /** * 具体驱动代码中实现如下所示 */ module_platform_driver(xxx_driver);
由以上展开可以看出，module_platform_driver是由module_driver封装而来，并填充了platform_driver_register、platform_driver_unregister两个函数作为宏的参数传递给了 module_driver的宏，这样做的目的是统一了接口函数，使得所有驱动的注册、注销函数都能统一的管理。
因此，展开 module_platform_driver(xxx_driver)，第一步展开，调用宏module_driver(xxx_driver，platform_driver_register，platform_driver_unregister)；第二步展开是展开宏module_driver，展开的结果是（在宏定义里，## 的作用是将连个参数连在一起， # 的作用是加上双引号）：
static int __init xxx_init(void) { return platform_driver_register(&xxx); } module_init( xxx_init); static void __exit xxx_init(void) { return platform_driver_unregister(& xxx); } module_exit( xxx_exit);
通过以上分析可知module_platform_driver这个宏是间接调用了platform_driver_register()和 platform_driver_unregister()实现了 驱动函数的注册和注销操作。
