本文轉載自:http://blog.csdn.net/eastmoon502136/article/details/37569789

?就像學編程第一個范例helloworld一樣，學嵌入式，單片機、fpga之類的第一個范例就是點亮一盞燈。對于龐大的Linux系統，當然可以編寫一個字符設備驅動來實現我們需要的led燈，也可以直接利用gpio口，應用程序來拉高拉低管腳控制。不過，既然linux系統自己本來就帶有led子系統，那么就可以好好利用之。好處不用多說了，主要對于應用層來說，不同平臺都用linux的led子系統，那么應用程序不用做任何的改變，就可以在新的平臺上運行，可移植性好。

???????? linux的led子系統的源碼路徑：

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Include/Linux/leds.h??

drivers/leds??

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???????? 首先看一下led子系統中的主要文件：

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#?LED?Core??

obj-$(CONFIG_NEW_LEDS)????????????????????????+=led-core.o??

obj-$(CONFIG_LEDS_CLASS)?????????????????+=?led-class.o??

obj-$(CONFIG_LEDS_TRIGGERS)??????????????+=led-triggers.o??

???

#?LED?PlatformDrivers??

obj-$(CONFIG_LEDS_GPIO)????????????????????????+=?leds-gpio.o??

???

#?LED?Triggers??

obj-$(CONFIG_LEDS_TRIGGER_TIMER)?+=ledtrig-timer.o??

obj-$(CONFIG_LEDS_TRIGGER_IDE_DISK)??????+=ledtrig-ide-disk.o??

obj-$(CONFIG_LEDS_TRIGGER_HEARTBEAT)?+=ledtrig-heartbeat.o??

obj-$(CONFIG_LEDS_TRIGGER_BACKLIGHT)?+=ledtrig-backlight.o??

obj-$(CONFIG_LEDS_TRIGGER_GPIO)??????????????+=ledtrig-gpio.o??

obj-$(CONFIG_LEDS_TRIGGER_DEFAULT_ON)????????+=?ledtrig-default-on.o??

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主要由leds.h、led-core.c、led-class.c、led-triggers.c，其中led-triggers又分為了timer、ide-disk、heartbeat、backlight、gpio、default-on等算法。

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例子程序是leds-gpio，接下去會主要分析這個驅動實現。

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首先簡單看一下主要的文件

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Leds.h

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1、enum?led_brightness{??

?????????LED_OFF???????????=?0,??

?????????LED_HALF?????????=?127,??

?????????LED_FULL?????????=?255,??

};??

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Led的亮度，分為三等級，關、中間、最亮。

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2、struct?led_classdev{??

?????????constchar??????????????????*name;???//?Led的名字??

?????????int???????????????????????brightness;???//led亮度??

?????????int???????????????????????max_brightness;?//led最大亮度??

?????????int???????????????????????flags;??

???

?????????/*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,??

?????????????????????????????????????????????????enum?led_brightness?brightness);???//亮度設置函數指針??

?????????/*Get?LED?brightness?level?*/??

?????????enumled_brightness?(*brightness_get)(struct?led_classdev?*led_cdev);?//獲取亮度函數指針??

???

?????????int??????????????(*blink_set)(struct?led_classdev*led_cdev,??

??????????????????????????????????????????unsigned?long?*delay_on,??

??????????????????????????????????????????unsigned?long?*delay_off);??//閃爍時點亮和熄滅的時間設置??

???

?????????structdevice?????????????*dev;??

?????????structlist_head????????node;????????????????????????//leds-list的node??

?????????constchar??????????????????*default_trigger;?????//默認trigger的名字??

???

?????????unsignedlong???????????blink_delay_on,blink_delay_off;???//閃爍的開關時間??

?????????structtimer_list???????blink_timer;????????????????????//閃爍的定時器鏈表??

?????????int???????????????????????blink_brightness;???????????????????//閃爍的亮度??

???

#ifdef?CONFIG_LEDS_TRIGGERS??

?????????/*Protects?the?trigger?data?below?*/??

?????????structrw_semaphore??????trigger_lock;???????????????//trigger的鎖??

???

?????????structled_trigger????*trigger;??????????????????????//led的trigger??

?????????structlist_head????????trig_list;?????????????????????//trigger的鏈表??

?????????void????????????????????*trigger_data;?????????????????????//trigger的數據??

#endif??

};??

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3、struct?led_trigger?{??

?????????/*Trigger?Properties?*/??

?????????constchar????????*name;???????????//trigger的名字??

?????????void???????????(*activate)(struct?led_classdev*led_cdev);???//激活trigger??

?????????void???????????(*deactivate)(struct?led_classdev*led_cdev);????

???

?????????/*LEDs?under?control?by?this?trigger?(for?simple?triggers)?*/??

?????????rwlock_t???leddev_list_lock;??

?????????structlist_head??led_cdevs;?????????????????????//led設備的鏈表??

???

?????????/*Link?to?next?registered?trigger?*/??

?????????structlist_head??next_trig;??

};??

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4、/*?For?the?leds-gpiodriver?*/??

struct?gpio_led?{??

?????????constchar?*name;??????????????//led的名字??

?????????constchar?*default_trigger;????????????//默認的trigger??

?????????unsigned?????????gpio;????????????????????????????//gpio口??

?????????unsigned??active_low?:?1;?????????

?????????unsigned??retain_state_suspended?:?1;??

?????????unsigned??default_state?:?2;??

?????????/*default_state?should?be?one?of?LEDS_GPIO_DEFSTATE_(ON|OFF|KEEP)?*/??

};??

???

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5、structgpio_led_platform_data?{??

?????????int???????????num_leds;?????????????led的個數??

?????????conststruct?gpio_led?*leds;???????led結構體??

???

#define?GPIO_LED_NO_BLINK_LOW???????0???????/*No?blink?GPIO?state?low?*/??

#define?GPIO_LED_NO_BLINK_HIGH??????1???????/*No?blink?GPIO?state?high?*/??

#define?GPIO_LED_BLINK?????????????????2???????/*?Please,?blink?*/??

?????????int??????????????(*gpio_blink_set)(unsigned?gpio,int?state,??

???????????????????????????????????????????????unsignedlong?*delay_on,??

???????????????????????????????????????????????unsignedlong?*delay_off);??

};??

???

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led-core.c

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DECLARE_RWSEM(leds_list_lock);??

EXPORT_SYMBOL_GPL(leds_list_lock);??

???

LIST_HEAD(leds_list);??

EXPORT_SYMBOL_GPL(leds_list);??

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主要是聲明了leds的鏈表和鎖。

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Led-class.c

1、? leds_init

主要是創建leds_class，賦值suspend和resume以及dev_attrs。

led_class_attrs

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static??struct?device_attribute?led_class_attrs[]?=?{??

?????????__ATTR(brightness,0644,?led_brightness_show,?led_brightness_store),??

?????????__ATTR(max_brightness,0444,?led_max_brightness_show,?NULL),??

#ifdef?CONFIG_LEDS_TRIGGERS??

?????????__ATTR(trigger,0644,?led_trigger_show,?led_trigger_store),??

#endif??

?????????__ATTR_NULL,??

};??

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2、led_classdev_register

???????? 創建classdev設備，也即Leds_class類中實例化一個對象，類似于c++的new一個對象，leds有很多種，而這里是注冊一個特定的led，內核中的面向對象思想也極其豐富。

???????? 加到leds_list鏈表中，初始化blinktimer，指定blink_timer的function和data，設置trigger，然后一個新的led設備就注冊好了，就可以使用了。

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led-triggers.c

1、led_trigger_register

???????? 掃描trigger鏈表中是否有同名的trigger，接著把當前trigger加入到鏈表中，如果led_classdev中有默認的trigger，那么就設置這個默認的。

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好了，簡單看了下led子系統中比較重要的結構體和函數，那么接下去就可以通過leds-gpio這個驅動來進一步了解led子系統了。

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