Android按键灯流程分析

alps\frameworks\base\services\java\com\Android\server\LightsService.java

使用方法：
private LightsService.Light mButtonLight;
mButtonLight = mLightsService.getLight(LightsService.LIGHT_ID_BUTTONS);
mButtonLight.setBrightness(screenBrightness);
mButtonLight.turnOff();

本地代码在：
alps\frameworks\base\services\jni\com_android_server_LightsService.cpp

接口关联使用：
static JNINativeMethod method_table[] = {
    { "init_native", "()I", (void*)init_native },
    { "finalize_native", "(I)V", (void*)finalize_native },
    { "setLight_native", "(IIIIIII)V", (void*)setLight_native },
};

int register_android_server_LightsService(JNIEnv *env)
{
    return jniRegisterNativeMethods(env, "com/android/server/LightsService",
            method_table, NELEM(method_table));
}

register_android_server_LightsService函数在alps\frameworks\base\services\jni\onload.cpp里面注册

本地c代码在：
alps\mediatek\hardware\liblights\lights.c里面open_lights里面

static int
set_light_buttons(struct light_device_t* dev,
        struct light_state_t const* state)
{
    int err = 0;
    int on = is_lit(state);
    pthread_mutex_lock(&g_lock);
    g_buttons = on;
    err = write_int(BUTTON_FILE, on?255:0);
    pthread_mutex_unlock(&g_lock);
    return err;
}

com_android_server_LightsService.cp里面使用 devices->lights[light]->set_light(devices->lights[light], &state);来调用真正的代码
如果有root机子，可以如下测试：
 echo 0 > /sys/class/leds/button-backlight/brightness  关按键灯
  echo 1 > /sys/class/leds/button-backlight/brightness  开按键灯
 
  echo 0 > /sys/class/leds/button-backlight/brightness 执行的意思为：输出0，作为/sys/class/leds/button-backlight/brightness的输入传入。
  如此便会打开brightness设备，并执行write将0带入执行。

相关阅读：

按键从Linux到Android

Android 4.0中按键的处理流程

Android 中如何监听按键的长按事件 

Android输入法框架中按键消息的处理流程