Android 亮度调节

frameworks/base/packages/SystemUI/src/com/android/systemui/settings/BrightnessController.java
更新屏幕亮度值Settings.System.SCREEN_BRIGHTNESS
BrightnessController.java中有个onChanged事件，这个是更新 setBrightness(val)

   private void setBrightness(int brightness) {
        try {
            mPower.setTemporaryScreenBrightnessSettingOverride(brightness);
        } catch (RemoteException ex) {
        }
    }

frameworks/base/services/java/com/android/server/power/PowerManagerService.java

setTemporaryScreenBrightnessSettingOverrideInternal
            updatePowerStateLocked
                updateDisplayPowerStateLocked
                       mDisplayPowerController.requestPowerState

frameworks/base/services/java/com/android/server/power/DisplayPowerController.java

requestPowerState
      sendUpdatePowerStateLocked
              updatePowerState
                    setScreenOn
                         mPowerState.setScreenOn

/frameworks/base/services/java/com/android/server/power/DisplayPowerState.java

setScreenOn
     scheduleScreenUpdate
        postScreenUpdateThreadSafe
              mHandler.post(mScreenUpdateRunnable)
                     mPhotonicModulator.setState(mScreenOn, brightness)
                          AsyncTask.THREAD_POOL_EXECUTOR.execute(mTask)
                                 mBacklight.setBrightness
（mBacklight类是LightsService.Light）LightsService.Light

DisplayPowerState是和LightService交互的，LightService是和HAL层的lights.c或lights.cpp和内核交互

frameworks/base/services/java/com/android/server/LightsService.java

setBrightness

    setLightLocked

         setLight_native

/frameworks/base/services/jni/com_android_server_LightsService.cpp

setLight_native

  devices->lights[light]->set_light(devices->lights[light], &state);

接下来就HAL层的处理，每个产商有所差异，找到LIGHTS_HARDWARE_MODULE_ID的定义

/device/softwinner/t3-common/hardware/libhardware/lights/lights.c

open_lights

内核里面生成结点：/dev/disp，通过ioctl到内核中去设置PWM引脚的值

参考

https://blog.youkuaiyun.com/fightfightfight/article/details/83548710

https://blog.youkuaiyun.com/FightFightFight/article/details/81320519