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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-$(CONFIG_NEW_LEDS) += led-core.o
obj-$(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;}
函数在/sys/class目录下产生了leds这个子目录，按照led模型注册的设备都会出现在该目录下
static struct device_attribute led_class_attrs[] = { __ATTR(brightness, 0644, led_brightness_show, led_brightness_store), __ATTR(max_brightness, 0644, led_max_brightness_show, led_max_brightness_store),#ifdef CONFIG_LEDS_TRIGGERS __ATTR(trigger, 0644, led_trigger_show, led_trigger_store),#endif __ATTR_NULL,
};
可见，属性函数的通用设置函数为led_brightness_store，获得函数位led_brightness_show，大同小异：
static ssize_t led_brightness_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t size){ struct led_classdev *led_cdev = dev_get_drvdata(dev); //获得led设备信息 ssize_t ret = -EINVAL; char *after; unsigned long state = simple_strtoul(buf, &after, 10); size_t count = after - buf; if (isspace(*after)) count++; if (count == size) { ret = count; if (state == LED_OFF) led_trigger_remove(led_cdev); led_set_brightness(led_cdev, state); } return ret;
}
跟进一下led_set_brightness函数：
static inline void led_set_brightness(struct led_classdev *led_cdev, enum led_brightness value){ if (value > led_cdev->max_brightness) value = led_cdev->max_brightness; led_cdev->brightness = value; if (!(led_cdev->flags & LED_SUSPENDED)) {#ifdef CONFIG_HAS_EARLYSUSPEND if (queue_brightness_change(led_cdev, value) != 0)#endif led_cdev->brightness_set(led_cdev, value); }}
可见最终确实是回调的 led_cdev->brightness_set来完成的该属性的设置。
下面看一下给我们留的接口，注册函数：
int led_classdev_register(struct device *parent, struct led_classdev *led_cdev){ led_cdev->dev = device_create(leds_class, parent, 0, led_cdev, "%s", led_cdev->name); //在leds目录下产生该设备的目录项 if (IS_ERR(led_cdev->dev)) return PTR_ERR(led_cdev->dev);#ifdef CONFIG_LEDS_TRIGGERS init_rwsem(&led_cdev->trigger_lock);#endif /* add to the list of leds */ down_write(&leds_list_lock); list_add_tail(&led_cdev->node, &leds_list); //把该设备加入全局链表 up_write(&leds_list_lock); if (!led_cdev->max_brightness) led_cdev->max_brightness = LED_FULL; //最大值如果没设置，则设置成255 led_update_brightness(led_cdev); #ifdef CONFIG_LEDS_TRIGGERS led_trigger_set_default(led_cdev);#endif printk(KERN_DEBUG "Registered led device: %s\n", led_cdev->name); return 0;}
总结：基本上简要分析了一下led子系统，代码不多，也很容易看，主要自己端的probe函数要配置好io口的功能，填充好led_cdev这个东东，然后注册就可以了 ^.^~
转载于:https://www.cnblogs.com/cxt-janson/p/4227194.html
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