platform驱动平台下，关于probe函数中，形参dev的“dev-＞dev.of_node；”的理解

        驱动函数里通过int platform_driver_register (struct platform_driver *driver)函数注册的驱动， 

183 static int __init miscbeep_init(void)
184 {
185 return platform_driver_register(&beep_driver);
186 }

198 module_init(miscbeep_init);

当platform总线检测到设备树有和该驱动匹配的设备节点后，就执行probe函数(  int (*probe) (struct device *dev); )，此时probe函数的形参dev指针指向的变量是platform_device类型，platform_device结构体保存的是platform平台下的设备信息。

22 struct platform_device {
23 const char *name; 
24 int id; 
25 bool id_auto;
26 struct device dev;
27 u32 num_resources; 
28 struct resource *resource;
29
30 const struct platform_device_id *id_entry;
31 char *driver_override; /* Driver name to force a match */
32
33 /* MFD cell pointer */
34 struct mfd_cell *mfd_cell;
35
36 /* arch specific additions */
37 struct pdev_archdata archdata;
38 };

        其 26行的“struct device dev” 成员(类似于C++的父类，platform_device继承了struct device )已经获取到了设备树中的节点信息，可以通过此成员获取节点信息，即“ miscbeep.nd = dev->dev.of_node;”

static int miscbeep_probe(struct platform_device *dev)
 {
 int ret = 0;

 printk("beep driver and device was matched!\r\n");
 /* 设置 BEEP 所使用的 GPIO */
 /* 1、获取设备节点：beep */
 //miscbeep.nd = of_find_node_by_path("/beep");
 
 miscbeep.nd = dev->dev.of_node;//用这种方式替代上一行“miscbeep.nd = of_find_node_by_path("/beep");”的方式来获取设备节点

device结构体：设备驱动模型中的基础结构体之一。结构体定义如下：

struct device {

　　/*设备所依附的父设备，大多数情况下，这样的设备是某种总线或主控制器，如果该成员变量的值为NULL，表示当前设备是一个最顶端设备，通常这样的设备都不是你想得到的那个*/

　　struct device *parent;

　　struct device_private *p;

　　struct kobject kobj;
　　const char *init_name; /* initial name of the device */
　　const struct device_type *type;

　　struct mutex mutex; /* mutex to synchronize calls to  its driver.*/

　　struct bus_type *bus; /* type of bus device is on */
　　struct device_driver *driver; /* which driver has allocated this device */
　　void *platform_data; /* Platform specific data, device core doesn't touch it */
　　 struct dev_pm_info power;
　　struct dev_pm_domain *pm_domain;

#ifdef CONFIG_NUMA
　　int numa_node; /* NUMA node this device is close to */
#endif
　　u64 *dma_mask; /* dma mask (if dma'able device) */
　　u64 coherent_dma_mask;/* Like dma_mask, but for alloc_coherent mappings as not all hardware supports
64 bit addresses for consistent  allocations such descriptors. */

　　struct device_dma_parameters *dma_parms;

　　struct list_head dma_pools; /* dma pools (if dma'ble) */

　　struct dma_coherent_mem *dma_mem; /* internal for coherent mem override */
/* arch specific additions */
　　struct dev_archdata archdata;

　　struct device_node *of_node; /* associated device tree node */

　　dev_t devt; /* dev_t, creates the sysfs "dev" */
　　u32 id; /* device instance */

　　spinlock_t devres_lock;
　　struct list_head devres_head;

　　struct klist_node knode_class;
　　struct class *class;
　　const struct attribute_group **groups; /* optional groups */

　　void (*release)(struct device *dev);
};