Linux设备模型之led子系统
时代不同了，连led都成子系统了，针对内核提供的通用模型，分析一下，好久没写文章了也！
代码位于drivers/leds下，看一下Makefile 模型文件主要是：
# LED Core
obj-$(CONFIG_LEDS_CLASS) += led-class.o
obj-$(CONFIG_LEDS_TRIGGERS) += led-triggers.o
直接看led-core文件吧，这个文件无比个性，主体内容四行
DECLARE_RWSEM(leds_list_lock);
EXPORT_SYMBOL_GPL(leds_list_lock);
LIST_HEAD(leds_list); //链接所有led的全局链表
EXPORT_SYMBOL_GPL(leds_list);
再来看下led-class.c函数，这里先来介绍一下描述led的核心结构体
struct led_classdev {
const char *name; //名字
int brightness; //亮度值，也可以用来表示开关特性
int max_brightness; //允许的最大亮度值
int flags; //标志
/* Lower 16 bits reflect status */
#define LED_SUSPENDED (1 << 0)
/* Upper 16 bits reflect control information */
#define LED_CORE_SUSPENDRESUME (1 << 16)
/* Set LED brightness level */
/* Must not sleep, use a workqueue if needed */
void (*brightness_set)(struct led_classdev *led_cdev, //核心回调函数，当设置/sys/class/leds/下的led接口里的brightness属性文件时，会回调该函数
enum led_brightness brightness);
/* Get LED brightness level */
enum led_brightness (*brightness_get)(struct led_classdev *led_cdev); //核心回调函数，当获得led当前值时会调用
/* Activate hardware accelerated blink, delays are in
* miliseconds and if none is provided then a sensible default
* should be chosen. The call can adjust the timings if it can't
* match the values specified exactly. */
int (*blink_set)(struct led_classdev *led_cdev,
unsigned long *delay_on,
unsigned long *delay_off);
struct device *dev; //嵌入的标准设备模型
struct list_head node; /* LED Device list */ //上面提到的全局led设备的挂接点
const char *default_trigger; /* Trigger to use */
#ifdef CONFIG_LEDS_TRIGGERS
/* Protects the trigger data below */
struct rw_semaphore trigger_lock;
struct led_trigger *trigger;
struct list_head trig_list;
void *trigger_data;
#endif
};
好了，下面说下初始化函数：
static int __init leds_init(void){
leds_class = class_create(THIS_MODULE, "leds");
if (IS_ERR(leds_class))
return PTR_ERR(leds_class);
leds_class->suspend = led_suspend;
leds_class->resume = led_resume;
leds_class->dev_attrs = led_class_attrs; //属性文件，sys下的接口，重点看一下
return 0;
}