From e048d65f45e14d7b7c1f2d84d7da31d6efe081c7 Mon Sep 17 00:00:00 2001
From: Vaibhav Devmurari <vdevmurari@google.com>
Date: Thu, 25 May 2023 17:09:19 +0000
Subject: [PATCH] Add ALS controlled keyboard backlight support

DD: go/pk_ambient_backlight_control
Bug: 262039362
Test: atest FrameworksServicesTests:AmbientKeyboardBacklightControllerTests
Test: atest FrameworksServicesTests:KeyboardBacklightControllerTests
Change-Id: I5254d7db06f0beedeab59c0cc69dd3d8d046a152
---
 .../display/DisplayManagerInternal.java       |  28 ++
 core/res/res/values/config.xml                |  50 +-
 core/res/res/values/symbols.xml               |   5 +-
 .../server/display/DisplayManagerService.java |  16 +
 .../AmbientKeyboardBacklightController.java   | 431 ++++++++++++++++++
 .../input/InputFeatureFlagProvider.java       |  19 +-
 .../input/KeyboardBacklightController.java    | 150 ++++--
 ...AmbientKeyboardBacklightControllerTests.kt | 355 +++++++++++++++
 .../input/KeyboardBacklightControllerTests.kt | 237 +++++++++-
 9 files changed, 1230 insertions(+), 61 deletions(-)
 create mode 100644 services/core/java/com/android/server/input/AmbientKeyboardBacklightController.java
 create mode 100644 services/tests/servicestests/src/com/android/server/input/AmbientKeyboardBacklightControllerTests.kt

diff --git a/core/java/android/hardware/display/DisplayManagerInternal.java b/core/java/android/hardware/display/DisplayManagerInternal.java
index d6df033212983..94bff893b5a85 100644
--- a/core/java/android/hardware/display/DisplayManagerInternal.java
+++ b/core/java/android/hardware/display/DisplayManagerInternal.java
@@ -412,6 +412,15 @@ public abstract class DisplayManagerInternal {
     @Nullable
     public abstract HostUsiVersion getHostUsiVersion(int displayId);
 
+    /**
+     * Get the ALS data for a particular display.
+     *
+     * @param displayId The id of the display.
+     * @return {@link AmbientLightSensorData}
+     */
+    @Nullable
+    public abstract AmbientLightSensorData getAmbientLightSensorData(int displayId);
+
     /**
      * Get all available DisplayGroupIds.
      */
@@ -669,4 +678,23 @@ public abstract class DisplayManagerInternal {
             return "RefreshRateLimitation(" + type + ": " + range + ")";
         }
     }
+
+    /**
+     * Class to provide Ambient sensor data using the API
+     * {@link DisplayManagerInternal#getAmbientLightSensorData(int)}
+     */
+    public static final class AmbientLightSensorData {
+        public String sensorName;
+        public String sensorType;
+
+        public AmbientLightSensorData(String name, String type) {
+            sensorName = name;
+            sensorType = type;
+        }
+
+        @Override
+        public String toString() {
+            return "AmbientLightSensorData(" + sensorName + ", " + sensorType + ")";
+        }
+    }
 }
diff --git a/core/res/res/values/config.xml b/core/res/res/values/config.xml
index 8473f9bc8d0b7..828e7aa765660 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -1675,16 +1675,56 @@
          in the config_autoBrightnessLevels array.  This array should have size one greater
          than the size of the config_autoBrightnessLevels array.
          The brightness values must be between 0 and 255 and be non-decreasing.
+
          This must be overridden in platform specific overlays -->
     <integer-array name="config_autoBrightnessButtonBacklightValues">
     </integer-array>
 
-    <!-- Array of output values for keyboard backlight corresponding to the lux values
-         in the config_autoBrightnessLevels array.  This array should have size one greater
-         than the size of the config_autoBrightnessLevels array.
-         The brightness values must be between 0 and 255 and be non-decreasing.
+    <!-- Smoothing constant for Ambient keyboard backlight change. It should contain value
+         in the range (0.0, 1.0] that will be used to calculate smoothed lux values using
+         simple exponential smoothing. This value indicated how quickly we transition to
+         the lux values provided by the Ambient light sensor.
+         Simple formula for newLuxValue = (1-constant)*currLuxValue + constant*rawLuxValue, where
+         rawLuxValue is the value provided by the Ambient light sensor. (e.g. value of 1.0 means we
+         immediately start using the value provided by the Ambient light sensor)
          This must be overridden in platform specific overlays -->
-    <integer-array name="config_autoBrightnessKeyboardBacklightValues">
+    <item name="config_autoKeyboardBrightnessSmoothingConstant" format="float" type="dimen">
+        1.0
+    </item>
+
+    <!-- Array of output values for keyboard backlight corresponding to the lux values
+         in the config_autoKeyboardBacklight(Increase/Decrease)LuxThreshold arrays.
+         The brightness values must be between 0 and 255 and be non-decreasing.
+
+         This can be overridden in platform specific overlays -->
+    <integer-array name="config_autoKeyboardBacklightBrightnessValues">
+        <item>102</item>
+        <item>153</item>
+        <item>0</item>
+    </integer-array>
+
+    <!-- Array of threshold values for keyboard backlight corresponding to the values
+         in the config_autoKeyboardBacklightBrightnessValues array.
+         These lux values indicate when to move to a lower keyboard backlight value,
+         as defined in config_autoKeyboardBacklightBrightnessValues array.
+
+         This can be overridden in platform specific overlays -->
+    <integer-array name="config_autoKeyboardBacklightDecreaseLuxThreshold">
+        <item>-1</item>
+        <item>40</item>
+        <item>150</item>
+    </integer-array>
+
+    <!-- Array of threshold values for keyboard backlight corresponding to the values
+         in the config_autoKeyboardBacklightBrightnessValues array.
+         These lux values indicate when to move to a higher keyboard backlight value,
+         as defined in config_autoKeyboardBacklightBrightnessValues array.
+
+         This can be overridden in platform specific overlays -->
+    <integer-array name="config_autoKeyboardBacklightIncreaseLuxThreshold">
+        <item>55</item>
+        <item>200</item>
+        <item>-1</item>
     </integer-array>
 
     <!-- An array describing the screen's backlight values corresponding to the brightness
diff --git a/core/res/res/values/symbols.xml b/core/res/res/values/symbols.xml
index 94225926896ba..d4b229eac2e32 100644
--- a/core/res/res/values/symbols.xml
+++ b/core/res/res/values/symbols.xml
@@ -520,6 +520,7 @@
   <java-symbol type="dimen" name="config_viewConfigurationHandwritingSlop" />
   <java-symbol type="dimen" name="config_viewConfigurationHoverSlop" />
   <java-symbol type="dimen" name="config_ambiguousGestureMultiplier" />
+  <java-symbol type="dimen" name="config_autoKeyboardBrightnessSmoothingConstant" />
   <java-symbol type="dimen" name="config_viewMinFlingVelocity" />
   <java-symbol type="dimen" name="config_viewMaxFlingVelocity" />
   <java-symbol type="dimen" name="config_viewMinRotaryEncoderFlingVelocity" />
@@ -1888,11 +1889,13 @@
   <java-symbol type="anim" name="dream_activity_open_enter" />
   <java-symbol type="anim" name="dream_activity_close_exit" />
   <java-symbol type="array" name="config_autoBrightnessButtonBacklightValues" />
-  <java-symbol type="array" name="config_autoBrightnessKeyboardBacklightValues" />
   <java-symbol type="array" name="config_autoBrightnessLcdBacklightValues" />
   <java-symbol type="array" name="config_autoBrightnessLcdBacklightValues_doze" />
   <java-symbol type="array" name="config_autoBrightnessLevels" />
   <java-symbol type="array" name="config_autoBrightnessLevelsIdle" />
+  <java-symbol type="array" name="config_autoKeyboardBacklightBrightnessValues" />
+  <java-symbol type="array" name="config_autoKeyboardBacklightDecreaseLuxThreshold" />
+  <java-symbol type="array" name="config_autoKeyboardBacklightIncreaseLuxThreshold" />
   <java-symbol type="array" name="config_ambientThresholdLevels" />
   <java-symbol type="array" name="config_ambientBrighteningThresholds" />
   <java-symbol type="array" name="config_ambientDarkeningThresholds" />
diff --git a/services/core/java/com/android/server/display/DisplayManagerService.java b/services/core/java/com/android/server/display/DisplayManagerService.java
index c559ed867dd30..3832e6e372c52 100644
--- a/services/core/java/com/android/server/display/DisplayManagerService.java
+++ b/services/core/java/com/android/server/display/DisplayManagerService.java
@@ -4627,6 +4627,22 @@ public final class DisplayManagerService extends SystemService {
             }
         }
 
+        @Override
+        public AmbientLightSensorData getAmbientLightSensorData(int displayId) {
+            synchronized (mSyncRoot) {
+                final LogicalDisplay display = mLogicalDisplayMapper.getDisplayLocked(displayId);
+                if (display == null) {
+                    return null;
+                }
+                final DisplayDevice device = display.getPrimaryDisplayDeviceLocked();
+                if (device == null) {
+                    return null;
+                }
+                SensorData data = device.getDisplayDeviceConfig().getAmbientLightSensor();
+                return new AmbientLightSensorData(data.name, data.type);
+            }
+        }
+
         @Override
         public IntArray getDisplayGroupIds() {
             Set<Integer> visitedIds = new ArraySet<>();
diff --git a/services/core/java/com/android/server/input/AmbientKeyboardBacklightController.java b/services/core/java/com/android/server/input/AmbientKeyboardBacklightController.java
new file mode 100644
index 0000000000000..ce868497b0e4e
--- /dev/null
+++ b/services/core/java/com/android/server/input/AmbientKeyboardBacklightController.java
@@ -0,0 +1,431 @@
+/*
+ * Copyright 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.input;
+
+import android.annotation.MainThread;
+import android.annotation.Nullable;
+import android.content.Context;
+import android.content.res.Resources;
+import android.hardware.Sensor;
+import android.hardware.SensorEvent;
+import android.hardware.SensorEventListener;
+import android.hardware.SensorManager;
+import android.hardware.display.DisplayManager;
+import android.hardware.display.DisplayManagerInternal;
+import android.os.Handler;
+import android.os.Looper;
+import android.os.Message;
+import android.util.Log;
+import android.util.Slog;
+import android.util.TypedValue;
+import android.view.Display;
+import android.view.DisplayInfo;
+
+import com.android.internal.annotations.GuardedBy;
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.server.LocalServices;
+import com.android.server.display.utils.SensorUtils;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * A thread-safe component of {@link InputManagerService} responsible for managing the keyboard
+ * backlight based on ambient light sensor.
+ */
+final class AmbientKeyboardBacklightController implements DisplayManager.DisplayListener,
+        SensorEventListener {
+
+    private static final String TAG = "KbdBacklightController";
+
+    // To enable these logs, run:
+    // 'adb shell setprop log.tag.KbdBacklightController DEBUG' (requires restart)
+    private static final boolean DEBUG = Log.isLoggable(TAG, Log.DEBUG);
+
+    // Number of light sensor responses required to overcome temporal hysteresis.
+    @VisibleForTesting
+    public static final int HYSTERESIS_THRESHOLD = 2;
+
+    private static final int MSG_BRIGHTNESS_CALLBACK = 0;
+    private static final int MSG_SETUP_DISPLAY_AND_SENSOR = 1;
+
+    private static final Object sAmbientControllerLock = new Object();
+
+    private final Context mContext;
+    private final Handler mHandler;
+
+    @Nullable
+    @GuardedBy("sAmbientControllerLock")
+    private Sensor mLightSensor;
+    @GuardedBy("sAmbientControllerLock")
+    private String mCurrentDefaultDisplayUniqueId;
+
+    // List of currently registered ambient backlight listeners
+    @GuardedBy("sAmbientControllerLock")
+    private final List<AmbientKeyboardBacklightListener> mAmbientKeyboardBacklightListeners =
+            new ArrayList<>();
+
+    private BrightnessStep[] mBrightnessSteps;
+    private int mCurrentBrightnessStepIndex;
+    private HysteresisState mHysteresisState;
+    private int mHysteresisCount = 0;
+    private float mSmoothingConstant;
+    private int mSmoothedLux;
+    private int mSmoothedLuxAtLastAdjustment;
+
+    private enum HysteresisState {
+        // The most-recent mSmoothedLux matched mSmoothedLuxAtLastAdjustment.
+        STABLE,
+        // The most-recent mSmoothedLux was less than mSmoothedLuxAtLastAdjustment.
+        DECREASING,
+        // The most-recent mSmoothedLux was greater than mSmoothedLuxAtLastAdjustment.
+        INCREASING,
+        // The brightness should be adjusted immediately after the next sensor reading.
+        IMMEDIATE,
+    }
+
+    AmbientKeyboardBacklightController(Context context, Looper looper) {
+        mContext = context;
+        mHandler = new Handler(looper, this::handleMessage);
+        initConfiguration();
+    }
+
+    public void systemRunning() {
+        mHandler.sendEmptyMessage(MSG_SETUP_DISPLAY_AND_SENSOR);
+        DisplayManager displayManager = Objects.requireNonNull(
+                mContext.getSystemService(DisplayManager.class));
+        displayManager.registerDisplayListener(this, mHandler);
+    }
+
+    public void registerAmbientBacklightListener(AmbientKeyboardBacklightListener listener) {
+        synchronized (sAmbientControllerLock) {
+            if (mAmbientKeyboardBacklightListeners.contains(listener)) {
+                throw new IllegalStateException(
+                        "AmbientKeyboardBacklightListener was already registered, listener = "
+                                + listener);
+            }
+            if (mAmbientKeyboardBacklightListeners.isEmpty()) {
+                // Add sensor listener when we add the first ambient backlight listener.
+                addSensorListener(mLightSensor);
+            }
+            mAmbientKeyboardBacklightListeners.add(listener);
+        }
+    }
+
+    public void unregisterAmbientBacklightListener(AmbientKeyboardBacklightListener listener) {
+        synchronized (sAmbientControllerLock) {
+            if (!mAmbientKeyboardBacklightListeners.contains(listener)) {
+                throw new IllegalStateException(
+                        "AmbientKeyboardBacklightListener was never registered, listener = "
+                                + listener);
+            }
+            mAmbientKeyboardBacklightListeners.remove(listener);
+            if (mAmbientKeyboardBacklightListeners.isEmpty()) {
+                removeSensorListener(mLightSensor);
+            }
+        }
+    }
+
+    private void sendBrightnessAdjustment(int brightnessValue) {
+        Message msg = Message.obtain(mHandler, MSG_BRIGHTNESS_CALLBACK, brightnessValue);
+        mHandler.sendMessage(msg);
+    }
+
+    @MainThread
+    private void handleBrightnessCallback(int brightnessValue) {
+        synchronized (sAmbientControllerLock) {
+            for (AmbientKeyboardBacklightListener listener : mAmbientKeyboardBacklightListeners) {
+                listener.onKeyboardBacklightValueChanged(brightnessValue);
+            }
+        }
+    }
+
+    @MainThread
+    private void handleAmbientLuxChange(float rawLux) {
+        if (rawLux < 0) {
+            Slog.w(TAG, "Light sensor doesn't have valid value");
+            return;
+        }
+        updateSmoothedLux(rawLux);
+
+        if (mHysteresisState != HysteresisState.IMMEDIATE
+                && mSmoothedLux == mSmoothedLuxAtLastAdjustment) {
+            mHysteresisState = HysteresisState.STABLE;
+            return;
+        }
+
+        int newStepIndex = Math.max(0, mCurrentBrightnessStepIndex);
+        int numSteps = mBrightnessSteps.length;
+
+        if (mSmoothedLux > mSmoothedLuxAtLastAdjustment) {
+            if (mHysteresisState != HysteresisState.IMMEDIATE
+                    && mHysteresisState != HysteresisState.INCREASING) {
+                if (DEBUG) {
+                    Slog.d(TAG, "ALS transitioned to brightness increasing state");
+                }
+                mHysteresisState = HysteresisState.INCREASING;
+                mHysteresisCount = 0;
+            }
+            for (; newStepIndex < numSteps; newStepIndex++) {
+                if (mSmoothedLux < mBrightnessSteps[newStepIndex].mIncreaseLuxThreshold) {
+                    break;
+                }
+            }
+        } else if (mSmoothedLux < mSmoothedLuxAtLastAdjustment) {
+            if (mHysteresisState != HysteresisState.IMMEDIATE
+                    && mHysteresisState != HysteresisState.DECREASING) {
+                if (DEBUG) {
+                    Slog.d(TAG, "ALS transitioned to brightness decreasing state");
+                }
+                mHysteresisState = HysteresisState.DECREASING;
+                mHysteresisCount = 0;
+            }
+            for (; newStepIndex >= 0; newStepIndex--) {
+                if (mSmoothedLux > mBrightnessSteps[newStepIndex].mDecreaseLuxThreshold) {
+                    break;
+                }
+            }
+        }
+
+        if (mHysteresisState == HysteresisState.IMMEDIATE) {
+            mCurrentBrightnessStepIndex = newStepIndex;
+            mSmoothedLuxAtLastAdjustment = mSmoothedLux;
+            mHysteresisState = HysteresisState.STABLE;
+            mHysteresisCount = 0;
+            sendBrightnessAdjustment(mBrightnessSteps[newStepIndex].mBrightnessValue);
+            return;
+        }
+
+        if (newStepIndex == mCurrentBrightnessStepIndex) {
+            return;
+        }
+
+        mHysteresisCount++;
+        if (DEBUG) {
+            Slog.d(TAG, "Incremented hysteresis count to " + mHysteresisCount + " (lux went from "
+                    + mSmoothedLuxAtLastAdjustment + " to " + mSmoothedLux + ")");
+        }
+        if (mHysteresisCount >= HYSTERESIS_THRESHOLD) {
+            mCurrentBrightnessStepIndex = newStepIndex;
+            mSmoothedLuxAtLastAdjustment = mSmoothedLux;
+            mHysteresisCount = 1;
+            sendBrightnessAdjustment(mBrightnessSteps[newStepIndex].mBrightnessValue);
+        }
+    }
+
+    @MainThread
+    private void handleDisplayChange() {
+        DisplayManagerInternal displayManagerInternal = LocalServices.getService(
+                DisplayManagerInternal.class);
+        DisplayInfo displayInfo = displayManagerInternal.getDisplayInfo(Display.DEFAULT_DISPLAY);
+        synchronized (sAmbientControllerLock) {
+            if (Objects.equals(mCurrentDefaultDisplayUniqueId, displayInfo.uniqueId)) {
+                return;
+            }
+            if (DEBUG) {
+                Slog.d(TAG, "Default display changed: resetting the light sensor");
+            }
+            // Keep track of current default display
+            mCurrentDefaultDisplayUniqueId = displayInfo.uniqueId;
+            // Clear all existing sensor listeners
+            if (!mAmbientKeyboardBacklightListeners.isEmpty()) {
+                removeSensorListener(mLightSensor);
+            }
+            mLightSensor = getAmbientLightSensor(
+                    displayManagerInternal.getAmbientLightSensorData(Display.DEFAULT_DISPLAY));
+            // Re-add sensor listeners if required;
+            if (!mAmbientKeyboardBacklightListeners.isEmpty()) {
+                addSensorListener(mLightSensor);
+            }
+        }
+    }
+
+    private Sensor getAmbientLightSensor(
+            DisplayManagerInternal.AmbientLightSensorData ambientSensor) {
+        SensorManager sensorManager = Objects.requireNonNull(
+                mContext.getSystemService(SensorManager.class));
+        if (DEBUG) {
+            Slog.d(TAG, "Ambient Light sensor data: " + ambientSensor);
+        }
+        return SensorUtils.findSensor(sensorManager, ambientSensor.sensorType,
+                ambientSensor.sensorName, Sensor.TYPE_LIGHT);
+    }
+
+    private void updateSmoothedLux(float rawLux) {
+        // For the first sensor reading, use raw lux value directly without smoothing.
+        if (mHysteresisState == HysteresisState.IMMEDIATE) {
+            mSmoothedLux = (int) rawLux;
+        } else {
+            mSmoothedLux =
+                    (int) (mSmoothingConstant * rawLux + (1 - mSmoothingConstant) * mSmoothedLux);
+        }
+        if (DEBUG) {
+            Slog.d(TAG, "Current smoothed lux from ALS = " + mSmoothedLux);
+        }
+    }
+
+    @VisibleForTesting
+    public void addSensorListener(@Nullable Sensor sensor) {
+        SensorManager sensorManager = mContext.getSystemService(SensorManager.class);
+        if (sensorManager == null || sensor == null) {
+            return;
+        }
+        // Reset values before registering listener
+        reset();
+        sensorManager.registerListener(this, sensor, SensorManager.SENSOR_DELAY_NORMAL, mHandler);
+        if (DEBUG) {
+            Slog.d(TAG, "Registering ALS listener");
+        }
+    }
+
+    private void removeSensorListener(@Nullable Sensor sensor) {
+        SensorManager sensorManager = mContext.getSystemService(SensorManager.class);
+        if (sensorManager == null || sensor == null) {
+            return;
+        }
+        sensorManager.unregisterListener(this, sensor);
+        if (DEBUG) {
+            Slog.d(TAG, "Unregistering ALS listener");
+        }
+    }
+
+    private void initConfiguration() {
+        Resources res = mContext.getResources();
+        int[] brightnessValueArray = res.getIntArray(
+                com.android.internal.R.array.config_autoKeyboardBacklightBrightnessValues);
+        int[] decreaseThresholdArray = res.getIntArray(
+                com.android.internal.R.array.config_autoKeyboardBacklightDecreaseLuxThreshold);
+        int[] increaseThresholdArray = res.getIntArray(
+                com.android.internal.R.array.config_autoKeyboardBacklightIncreaseLuxThreshold);
+        if (brightnessValueArray.length != decreaseThresholdArray.length
+                || decreaseThresholdArray.length != increaseThresholdArray.length) {
+            throw new IllegalArgumentException(
+                    "The config files for auto keyboard backlight brightness must contain arrays "
+                            + "of equal lengths");
+        }
+        final int size = brightnessValueArray.length;
+        mBrightnessSteps = new BrightnessStep[size];
+        for (int i = 0; i < size; i++) {
+            int increaseThreshold =
+                    increaseThresholdArray[i] < 0 ? Integer.MAX_VALUE : increaseThresholdArray[i];
+            int decreaseThreshold =
+                    decreaseThresholdArray[i] < 0 ? Integer.MIN_VALUE : decreaseThresholdArray[i];
+            mBrightnessSteps[i] = new BrightnessStep(brightnessValueArray[i], increaseThreshold,
+                    decreaseThreshold);
+        }
+
+        int numSteps = mBrightnessSteps.length;
+        if (numSteps == 0 || mBrightnessSteps[0].mDecreaseLuxThreshold != Integer.MIN_VALUE
+                || mBrightnessSteps[numSteps - 1].mIncreaseLuxThreshold != Integer.MAX_VALUE) {
+            throw new IllegalArgumentException(
+                    "The config files for auto keyboard backlight brightness must contain arrays "
+                            + "of length > 0 and have -1 or Integer.MIN_VALUE as lower bound for "
+                            + "decrease thresholds and -1 or Integer.MAX_VALUE as upper bound for "
+                            + "increase thresholds");
+        }
+
+        final TypedValue smoothingConstantValue = new TypedValue();
+        res.getValue(
+                com.android.internal.R.dimen.config_autoKeyboardBrightnessSmoothingConstant,
+                smoothingConstantValue,
+                true /*resolveRefs*/);
+        mSmoothingConstant = smoothingConstantValue.getFloat();
+        if (mSmoothingConstant <= 0.0 || mSmoothingConstant > 1.0) {
+            throw new IllegalArgumentException(
+                    "The config files for auto keyboard backlight brightness must contain "
+                            + "smoothing constant in range (0.0, 1.0].");
+        }
+
+        if (DEBUG) {
+            Log.d(TAG, "Brightness steps: " + Arrays.toString(mBrightnessSteps)
+                    + " Smoothing constant = " + mSmoothingConstant);
+        }
+    }
+
+    private void reset() {
+        mHysteresisState = HysteresisState.IMMEDIATE;
+        mSmoothedLux = 0;
+        mSmoothedLuxAtLastAdjustment = 0;
+        mCurrentBrightnessStepIndex = -1;
+    }
+
+    private boolean handleMessage(Message msg) {
+        switch (msg.what) {
+            case MSG_BRIGHTNESS_CALLBACK:
+                handleBrightnessCallback((int) msg.obj);
+                return true;
+            case MSG_SETUP_DISPLAY_AND_SENSOR:
+                handleDisplayChange();
+                return true;
+        }
+        return false;
+    }
+
+    @Override
+    public void onSensorChanged(SensorEvent event) {
+        handleAmbientLuxChange(event.values[0]);
+    }
+
+    @Override
+    public void onAccuracyChanged(Sensor sensor, int accuracy) {
+    }
+
+    @Override
+    public void onDisplayAdded(int displayId) {
+        handleDisplayChange();
+    }
+
+    @Override
+    public void onDisplayRemoved(int displayId) {
+        handleDisplayChange();
+    }
+
+    @Override
+    public void onDisplayChanged(int displayId) {
+        handleDisplayChange();
+    }
+
+    public interface AmbientKeyboardBacklightListener {
+        /**
+         * @param value between [0, 255] to which keyboard backlight needs to be set according
+         *              to Ambient light sensor.
+         */
+        void onKeyboardBacklightValueChanged(int value);
+    }
+
+    private static class BrightnessStep {
+        private final int mBrightnessValue;
+        private final int mIncreaseLuxThreshold;
+        private final int mDecreaseLuxThreshold;
+
+        private BrightnessStep(int brightnessValue, int increaseLuxThreshold,
+                int decreaseLuxThreshold) {
+            mBrightnessValue = brightnessValue;
+            mIncreaseLuxThreshold = increaseLuxThreshold;
+            mDecreaseLuxThreshold = decreaseLuxThreshold;
+        }
+
+        @Override
+        public String toString() {
+            return "BrightnessStep{" + "mBrightnessValue=" + mBrightnessValue
+                    + ", mIncreaseThreshold=" + mIncreaseLuxThreshold + ", mDecreaseThreshold="
+                    + mDecreaseLuxThreshold + '}';
+        }
+    }
+}
diff --git a/services/core/java/com/android/server/input/InputFeatureFlagProvider.java b/services/core/java/com/android/server/input/InputFeatureFlagProvider.java
index 7c7f1513bd96f..a646d1e9bcb0f 100644
--- a/services/core/java/com/android/server/input/InputFeatureFlagProvider.java
+++ b/services/core/java/com/android/server/input/InputFeatureFlagProvider.java
@@ -39,14 +39,21 @@ public final class InputFeatureFlagProvider {
             InputProperties.enable_keyboard_backlight_animation().orElse(false);
 
     // To disable Custom keyboard backlight levels support via IDC files run:
-    // adb shell setprop persist.input.keyboard_backlight_custom_levels.enabled false (requires
+    // adb shell setprop persist.input.keyboard.backlight_custom_levels.enabled false (requires
     // restart)
     private static final boolean KEYBOARD_BACKLIGHT_CUSTOM_LEVELS_ENABLED =
             InputProperties.enable_keyboard_backlight_custom_levels().orElse(true);
 
+    // To disable als based ambient keyboard backlight control run:
+    // adb shell setprop persist.input.keyboard.ambient_backlight_control.enabled false (requires
+    // restart)
+    private static final boolean AMBIENT_KEYBOARD_BACKLIGHT_CONTROL_ENABLED =
+            InputProperties.enable_ambient_keyboard_backlight_control().orElse(true);
+
     private static Optional<Boolean> sKeyboardBacklightControlOverride = Optional.empty();
     private static Optional<Boolean> sKeyboardBacklightAnimationOverride = Optional.empty();
     private static Optional<Boolean> sKeyboardBacklightCustomLevelsOverride = Optional.empty();
+    private static Optional<Boolean> sAmbientKeyboardBacklightControlOverride = Optional.empty();
 
     public static boolean isKeyboardBacklightControlEnabled() {
         return sKeyboardBacklightControlOverride.orElse(KEYBOARD_BACKLIGHT_CONTROL_ENABLED);
@@ -61,6 +68,11 @@ public final class InputFeatureFlagProvider {
                 KEYBOARD_BACKLIGHT_CUSTOM_LEVELS_ENABLED);
     }
 
+    public static boolean isAmbientKeyboardBacklightControlEnabled() {
+        return sAmbientKeyboardBacklightControlOverride.orElse(
+                AMBIENT_KEYBOARD_BACKLIGHT_CONTROL_ENABLED);
+    }
+
     public static void setKeyboardBacklightControlEnabled(boolean enabled) {
         sKeyboardBacklightControlOverride = Optional.of(enabled);
     }
@@ -73,6 +85,10 @@ public final class InputFeatureFlagProvider {
         sKeyboardBacklightCustomLevelsOverride = Optional.of(enabled);
     }
 
+    public static void setAmbientKeyboardBacklightControlEnabled(boolean enabled) {
+        sAmbientKeyboardBacklightControlOverride = Optional.of(enabled);
+    }
+
     /**
      * Clears all input feature flag overrides.
      */
@@ -80,5 +96,6 @@ public final class InputFeatureFlagProvider {
         sKeyboardBacklightControlOverride = Optional.empty();
         sKeyboardBacklightAnimationOverride = Optional.empty();
         sKeyboardBacklightCustomLevelsOverride = Optional.empty();
+        sAmbientKeyboardBacklightControlOverride = Optional.empty();
     }
 }
diff --git a/services/core/java/com/android/server/input/KeyboardBacklightController.java b/services/core/java/com/android/server/input/KeyboardBacklightController.java
index 36238a8cfd230..1253b5b5b303c 100644
--- a/services/core/java/com/android/server/input/KeyboardBacklightController.java
+++ b/services/core/java/com/android/server/input/KeyboardBacklightController.java
@@ -18,6 +18,7 @@ package com.android.server.input;
 
 import android.animation.ValueAnimator;
 import android.annotation.BinderThread;
+import android.annotation.Nullable;
 import android.content.Context;
 import android.graphics.Color;
 import android.hardware.input.IKeyboardBacklightListener;
@@ -105,6 +106,12 @@ final class KeyboardBacklightController implements
     private final SparseArray<KeyboardBacklightListenerRecord> mKeyboardBacklightListenerRecords =
             new SparseArray<>();
 
+    private final AmbientKeyboardBacklightController mAmbientController;
+    @Nullable
+    private AmbientKeyboardBacklightController.AmbientKeyboardBacklightListener mAmbientListener;
+
+    private int mAmbientBacklightValue = 0;
+
     static {
         // Fixed brightness levels to avoid issues when converting back and forth from the
         // device brightness range to [0-255]
@@ -128,6 +135,7 @@ final class KeyboardBacklightController implements
         mDataStore = dataStore;
         mHandler = new Handler(looper, this::handleMessage);
         mAnimatorFactory = animatorFactory;
+        mAmbientController = new AmbientKeyboardBacklightController(context, looper);
     }
 
     @Override
@@ -151,6 +159,11 @@ final class KeyboardBacklightController implements
             }
         };
         observer.startObserving(UEVENT_KEYBOARD_BACKLIGHT_TAG);
+
+        if (InputFeatureFlagProvider.isAmbientKeyboardBacklightControlEnabled()) {
+            // Start ambient backlight controller
+            mAmbientController.systemRunning();
+        }
     }
 
     @Override
@@ -183,9 +196,21 @@ final class KeyboardBacklightController implements
         if (inputDevice == null || state == null) {
             return;
         }
-        Light keyboardBacklight = state.mLight;
         // Follow preset levels of brightness defined in BRIGHTNESS_LEVELS
-        final int currBrightnessLevel = state.mBrightnessLevel;
+        final int currBrightnessLevel;
+        if (state.mUseAmbientController) {
+            int index = Arrays.binarySearch(state.mBrightnessValueForLevel, mAmbientBacklightValue);
+            // Set current level to the lower bound of the ambient value in the brightness array.
+            if (index < 0) {
+                int lowerBound = Math.max(0, -(index + 1) - 1);
+                currBrightnessLevel =
+                        direction == Direction.DIRECTION_UP ? lowerBound : lowerBound + 1;
+            } else {
+                currBrightnessLevel = index;
+            }
+        } else {
+            currBrightnessLevel = state.mBrightnessLevel;
+        }
         final int newBrightnessLevel;
         if (direction == Direction.DIRECTION_UP) {
             newBrightnessLevel = Math.min(currBrightnessLevel + 1,
@@ -193,33 +218,67 @@ final class KeyboardBacklightController implements
         } else {
             newBrightnessLevel = Math.max(currBrightnessLevel - 1, 0);
         }
-        updateBacklightState(deviceId, newBrightnessLevel, true /* isTriggeredByKeyPress */);
 
+        state.setBrightnessLevel(newBrightnessLevel);
+
+        // Might need to stop listening to ALS since user has manually selected backlight
+        // level through keyboard up/down button
+        updateAmbientLightListener();
+
+        maybeBackupBacklightBrightness(inputDevice, state.mLight,
+                state.mBrightnessValueForLevel[newBrightnessLevel]);
+
+        if (DEBUG) {
+            Slog.d(TAG,
+                    "Changing state from " + state.mBrightnessLevel + " to " + newBrightnessLevel);
+        }
+
+        synchronized (mKeyboardBacklightListenerRecords) {
+            for (int i = 0; i < mKeyboardBacklightListenerRecords.size(); i++) {
+                IKeyboardBacklightState callbackState = new IKeyboardBacklightState();
+                callbackState.brightnessLevel = newBrightnessLevel;
+                callbackState.maxBrightnessLevel = state.getNumBrightnessChangeSteps();
+                mKeyboardBacklightListenerRecords.valueAt(i).notifyKeyboardBacklightChanged(
+                        deviceId, callbackState, true);
+            }
+        }
+    }
+
+    private void maybeBackupBacklightBrightness(InputDevice inputDevice, Light keyboardBacklight,
+            int brightnessValue) {
+        // Don't back up or restore when ALS based keyboard backlight is enabled
+        if (InputFeatureFlagProvider.isAmbientKeyboardBacklightControlEnabled()) {
+            return;
+        }
         synchronized (mDataStore) {
             try {
                 mDataStore.setKeyboardBacklightBrightness(inputDevice.getDescriptor(),
                         keyboardBacklight.getId(),
-                        state.mBrightnessValueForLevel[newBrightnessLevel]);
+                        brightnessValue);
             } finally {
                 mDataStore.saveIfNeeded();
             }
         }
     }
 
-    private void restoreBacklightBrightness(InputDevice inputDevice, Light keyboardBacklight) {
+    private void maybeRestoreBacklightBrightness(InputDevice inputDevice, Light keyboardBacklight) {
+        // Don't back up or restore when ALS based keyboard backlight is enabled
+        if (InputFeatureFlagProvider.isAmbientKeyboardBacklightControlEnabled()) {
+            return;
+        }
         KeyboardBacklightState state = mKeyboardBacklights.get(inputDevice.getId());
         OptionalInt brightness;
         synchronized (mDataStore) {
             brightness = mDataStore.getKeyboardBacklightBrightness(
                     inputDevice.getDescriptor(), keyboardBacklight.getId());
         }
-        if (brightness.isPresent()) {
+        if (state != null && brightness.isPresent()) {
             int brightnessValue = Math.max(0, Math.min(MAX_BRIGHTNESS, brightness.getAsInt()));
-            int index = Arrays.binarySearch(state.mBrightnessValueForLevel, brightnessValue);
-            if (index < 0) {
-                index = Math.min(state.getNumBrightnessChangeSteps(), -(index + 1));
+            int newLevel = Arrays.binarySearch(state.mBrightnessValueForLevel, brightnessValue);
+            if (newLevel < 0) {
+                newLevel = Math.min(state.getNumBrightnessChangeSteps(), -(newLevel + 1));
             }
-            updateBacklightState(inputDevice.getId(), index, false /* isTriggeredByKeyPress */);
+            state.setBrightnessLevel(newLevel);
             if (DEBUG) {
                 Slog.d(TAG, "Restoring brightness level " + brightness.getAsInt());
             }
@@ -260,6 +319,16 @@ final class KeyboardBacklightController implements
         } else {
             handleUserInactivity();
         }
+        updateAmbientLightListener();
+    }
+
+    @VisibleForTesting
+    public void handleAmbientLightValueChanged(int brightnessValue) {
+        mAmbientBacklightValue = brightnessValue;
+        for (int i = 0; i < mKeyboardBacklights.size(); i++) {
+            KeyboardBacklightState state = mKeyboardBacklights.valueAt(i);
+            state.onAmbientBacklightValueChanged();
+        }
     }
 
     private boolean handleMessage(Message msg) {
@@ -292,12 +361,14 @@ final class KeyboardBacklightController implements
     @Override
     public void onInputDeviceAdded(int deviceId) {
         onInputDeviceChanged(deviceId);
+        updateAmbientLightListener();
     }
 
     @VisibleForTesting
     @Override
     public void onInputDeviceRemoved(int deviceId) {
         mKeyboardBacklights.remove(deviceId);
+        updateAmbientLightListener();
     }
 
     @VisibleForTesting
@@ -318,7 +389,7 @@ final class KeyboardBacklightController implements
         }
         // The keyboard backlight was added or changed.
         mKeyboardBacklights.put(deviceId, new KeyboardBacklightState(deviceId, keyboardBacklight));
-        restoreBacklightBrightness(inputDevice, keyboardBacklight);
+        maybeRestoreBacklightBrightness(inputDevice, keyboardBacklight);
     }
 
     private InputDevice getInputDevice(int deviceId) {
@@ -379,30 +450,6 @@ final class KeyboardBacklightController implements
         }
     }
 
-    private void updateBacklightState(int deviceId, int brightnessLevel,
-            boolean isTriggeredByKeyPress) {
-        KeyboardBacklightState state = mKeyboardBacklights.get(deviceId);
-        if (state == null) {
-            return;
-        }
-
-        state.setBrightnessLevel(brightnessLevel);
-
-        synchronized (mKeyboardBacklightListenerRecords) {
-            for (int i = 0; i < mKeyboardBacklightListenerRecords.size(); i++) {
-                IKeyboardBacklightState callbackState = new IKeyboardBacklightState();
-                callbackState.brightnessLevel = brightnessLevel;
-                callbackState.maxBrightnessLevel = state.getNumBrightnessChangeSteps();
-                mKeyboardBacklightListenerRecords.valueAt(i).notifyKeyboardBacklightChanged(
-                        deviceId, callbackState, isTriggeredByKeyPress);
-            }
-        }
-
-        if (DEBUG) {
-            Slog.d(TAG, "Changing state from " + state.mBrightnessLevel + " to " + brightnessLevel);
-        }
-    }
-
     private void onKeyboardBacklightListenerDied(int pid) {
         synchronized (mKeyboardBacklightListenerRecords) {
             mKeyboardBacklightListenerRecords.remove(pid);
@@ -420,6 +467,25 @@ final class KeyboardBacklightController implements
         }
     }
 
+    private void updateAmbientLightListener() {
+        if (!InputFeatureFlagProvider.isAmbientKeyboardBacklightControlEnabled()) {
+            return;
+        }
+        boolean needToListenAmbientLightSensor = false;
+        for (int i = 0; i < mKeyboardBacklights.size(); i++) {
+            needToListenAmbientLightSensor |= mKeyboardBacklights.valueAt(i).mUseAmbientController;
+        }
+        needToListenAmbientLightSensor &= mIsInteractive;
+        if (needToListenAmbientLightSensor && mAmbientListener == null) {
+            mAmbientListener = this::handleAmbientLightValueChanged;
+            mAmbientController.registerAmbientBacklightListener(mAmbientListener);
+        }
+        if (!needToListenAmbientLightSensor && mAmbientListener != null) {
+            mAmbientController.unregisterAmbientBacklightListener(mAmbientListener);
+            mAmbientListener = null;
+        }
+    }
+
     private static boolean isValidBacklightNodePath(String devPath) {
         if (TextUtils.isEmpty(devPath)) {
             return false;
@@ -485,6 +551,8 @@ final class KeyboardBacklightController implements
         private int mBrightnessLevel;
         private ValueAnimator mAnimator;
         private final int[] mBrightnessValueForLevel;
+        private boolean mUseAmbientController =
+                InputFeatureFlagProvider.isAmbientKeyboardBacklightControlEnabled();
 
         KeyboardBacklightState(int deviceId, Light light) {
             mDeviceId = deviceId;
@@ -525,15 +593,25 @@ final class KeyboardBacklightController implements
         }
 
         private void onBacklightStateChanged() {
-            setBacklightValue(mIsBacklightOn ? mBrightnessValueForLevel[mBrightnessLevel] : 0);
+            int toValue = mUseAmbientController ? mAmbientBacklightValue
+                    : mBrightnessValueForLevel[mBrightnessLevel];
+            setBacklightValue(mIsBacklightOn ? toValue : 0);
         }
         private void setBrightnessLevel(int brightnessLevel) {
+            // Once we manually set level, disregard ambient light controller
+            mUseAmbientController = false;
             if (mIsBacklightOn) {
                 setBacklightValue(mBrightnessValueForLevel[brightnessLevel]);
             }
             mBrightnessLevel = brightnessLevel;
         }
 
+        private void onAmbientBacklightValueChanged() {
+            if (mIsBacklightOn && mUseAmbientController) {
+                setBacklightValue(mAmbientBacklightValue);
+            }
+        }
+
         private void cancelAnimation() {
             if (mAnimator != null && mAnimator.isRunning()) {
                 mAnimator.cancel();
diff --git a/services/tests/servicestests/src/com/android/server/input/AmbientKeyboardBacklightControllerTests.kt b/services/tests/servicestests/src/com/android/server/input/AmbientKeyboardBacklightControllerTests.kt
new file mode 100644
index 0000000000000..98b46286e9777
--- /dev/null
+++ b/services/tests/servicestests/src/com/android/server/input/AmbientKeyboardBacklightControllerTests.kt
@@ -0,0 +1,355 @@
+/*
+ * Copyright 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.input
+
+import android.content.Context
+import android.content.ContextWrapper
+import android.content.res.Resources
+import android.hardware.Sensor
+import android.hardware.SensorEvent
+import android.hardware.SensorEventListener
+import android.hardware.SensorManager
+import android.hardware.display.DisplayManagerInternal
+import android.hardware.input.InputSensorInfo
+import android.os.Handler
+import android.os.test.TestLooper
+import android.platform.test.annotations.Presubmit
+import android.util.TypedValue
+import android.view.Display
+import android.view.DisplayInfo
+import androidx.test.core.app.ApplicationProvider
+import com.android.internal.R
+import com.android.server.LocalServices
+import com.android.server.input.AmbientKeyboardBacklightController.HYSTERESIS_THRESHOLD
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertThrows
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.mockito.Mock
+import org.mockito.Mockito.any
+import org.mockito.Mockito.anyBoolean
+import org.mockito.Mockito.anyInt
+import org.mockito.Mockito.eq
+import org.mockito.Mockito.spy
+import org.mockito.Mockito.`when`
+import org.mockito.junit.MockitoJUnit
+
+/**
+ * Tests for {@link AmbientKeyboardBacklightController}.
+ *
+ * Build/Install/Run:
+ * atest FrameworksServicesTests:AmbientKeyboardBacklightControllerTests
+ */
+@Presubmit
+class AmbientKeyboardBacklightControllerTests {
+
+    companion object {
+        const val DEFAULT_DISPLAY_UNIQUE_ID = "uniqueId_1"
+        const val SENSOR_NAME = "test_sensor_name"
+        const val SENSOR_TYPE = "test_sensor_type"
+    }
+
+    @get:Rule
+    val rule = MockitoJUnit.rule()!!
+
+    private lateinit var context: Context
+    private lateinit var testLooper: TestLooper
+    private lateinit var ambientController: AmbientKeyboardBacklightController
+
+    @Mock
+    private lateinit var resources: Resources
+
+    @Mock
+    private lateinit var lightSensorInfo: InputSensorInfo
+
+    @Mock
+    private lateinit var sensorManager: SensorManager
+
+    @Mock
+    private lateinit var displayManagerInternal: DisplayManagerInternal
+    private lateinit var lightSensor: Sensor
+
+    private var currentDisplayInfo = DisplayInfo()
+    private var lastBrightnessCallback: Int = 0
+    private var listenerRegistered: Boolean = false
+    private var listenerRegistrationCount: Int = 0
+
+    @Before
+    fun setup() {
+        context = spy(ContextWrapper(ApplicationProvider.getApplicationContext()))
+        `when`(context.resources).thenReturn(resources)
+        setupBrightnessSteps()
+        setupSensor()
+        testLooper = TestLooper()
+        ambientController = AmbientKeyboardBacklightController(context, testLooper.looper)
+        ambientController.systemRunning()
+        testLooper.dispatchAll()
+    }
+
+    private fun setupBrightnessSteps() {
+        val brightnessValues = intArrayOf(100, 200, 0)
+        val decreaseThresholds = intArrayOf(-1, 900, 1900)
+        val increaseThresholds = intArrayOf(1000, 2000, -1)
+        `when`(resources.getIntArray(R.array.config_autoKeyboardBacklightBrightnessValues))
+            .thenReturn(brightnessValues)
+        `when`(resources.getIntArray(R.array.config_autoKeyboardBacklightDecreaseLuxThreshold))
+            .thenReturn(decreaseThresholds)
+        `when`(resources.getIntArray(R.array.config_autoKeyboardBacklightIncreaseLuxThreshold))
+            .thenReturn(increaseThresholds)
+        `when`(
+            resources.getValue(
+                eq(R.dimen.config_autoKeyboardBrightnessSmoothingConstant),
+                any(TypedValue::class.java),
+                anyBoolean()
+            )
+        ).then {
+            val args = it.arguments
+            val outValue = args[1] as TypedValue
+            outValue.data = java.lang.Float.floatToRawIntBits(1.0f)
+            Unit
+        }
+    }
+
+    private fun setupSensor() {
+        LocalServices.removeServiceForTest(DisplayManagerInternal::class.java)
+        LocalServices.addService(DisplayManagerInternal::class.java, displayManagerInternal)
+        currentDisplayInfo.uniqueId = DEFAULT_DISPLAY_UNIQUE_ID
+        `when`(displayManagerInternal.getDisplayInfo(Display.DEFAULT_DISPLAY)).thenReturn(
+            currentDisplayInfo
+        )
+        val sensorData = DisplayManagerInternal.AmbientLightSensorData(SENSOR_NAME, SENSOR_TYPE)
+        `when`(displayManagerInternal.getAmbientLightSensorData(Display.DEFAULT_DISPLAY))
+            .thenReturn(sensorData)
+
+        `when`(lightSensorInfo.name).thenReturn(SENSOR_NAME)
+        `when`(lightSensorInfo.stringType).thenReturn(SENSOR_TYPE)
+        lightSensor = Sensor(lightSensorInfo)
+        `when`(context.getSystemService(eq(Context.SENSOR_SERVICE))).thenReturn(sensorManager)
+        `when`(sensorManager.getSensorList(anyInt())).thenReturn(listOf(lightSensor))
+        `when`(
+            sensorManager.registerListener(
+                any(),
+                eq(lightSensor),
+                anyInt(),
+                any(Handler::class.java)
+            )
+        ).then {
+            listenerRegistered = true
+            listenerRegistrationCount++
+            true
+        }
+        `when`(
+            sensorManager.unregisterListener(
+                any(SensorEventListener::class.java),
+                eq(lightSensor)
+            )
+        ).then {
+            listenerRegistered = false
+            Unit
+        }
+    }
+
+    private fun setupSensorWithInitialLux(luxValue: Float) {
+        ambientController.registerAmbientBacklightListener { brightnessValue: Int ->
+            lastBrightnessCallback = brightnessValue
+        }
+        sendAmbientLuxValue(luxValue)
+        testLooper.dispatchAll()
+    }
+
+    @Test
+    fun testInitialAmbientLux_sendsCallbackImmediately() {
+        setupSensorWithInitialLux(500F)
+
+        assertEquals(
+            "Should receive immediate callback for first lux change",
+            100,
+            lastBrightnessCallback
+        )
+    }
+
+    @Test
+    fun testBrightnessIncrease_afterInitialLuxChanges() {
+        setupSensorWithInitialLux(500F)
+
+        // Current state: Step 1 [value = 100, increaseThreshold = 1000, decreaseThreshold = -1]
+        repeat(HYSTERESIS_THRESHOLD) {
+            sendAmbientLuxValue(1500F)
+        }
+        testLooper.dispatchAll()
+
+        assertEquals(
+            "Should receive brightness change callback for increasing lux change",
+            200,
+            lastBrightnessCallback
+        )
+    }
+
+    @Test
+    fun testBrightnessDecrease_afterInitialLuxChanges() {
+        setupSensorWithInitialLux(1500F)
+
+        // Current state: Step 2 [value = 200, increaseThreshold = 2000, decreaseThreshold = 900]
+        repeat(HYSTERESIS_THRESHOLD) {
+            sendAmbientLuxValue(500F)
+        }
+        testLooper.dispatchAll()
+
+        assertEquals(
+            "Should receive brightness change callback for decreasing lux change",
+            100,
+            lastBrightnessCallback
+        )
+    }
+
+    @Test
+    fun testRegisterAmbientListener_throwsExceptionOnRegisteringDuplicate() {
+        val ambientListener =
+            AmbientKeyboardBacklightController.AmbientKeyboardBacklightListener { }
+        ambientController.registerAmbientBacklightListener(ambientListener)
+
+        assertThrows(IllegalStateException::class.java) {
+            ambientController.registerAmbientBacklightListener(
+                ambientListener
+            )
+        }
+    }
+
+    @Test
+    fun testUnregisterAmbientListener_throwsExceptionOnUnregisteringNonExistent() {
+        val ambientListener =
+            AmbientKeyboardBacklightController.AmbientKeyboardBacklightListener { }
+        assertThrows(IllegalStateException::class.java) {
+            ambientController.unregisterAmbientBacklightListener(
+                ambientListener
+            )
+        }
+    }
+
+    @Test
+    fun testSensorListenerRegistered_onRegisterUnregisterAmbientListener() {
+        assertEquals(
+            "Should not have a sensor listener registered at init",
+            0,
+            listenerRegistrationCount
+        )
+        assertFalse("Should not have a sensor listener registered at init", listenerRegistered)
+
+        val ambientListener1 =
+            AmbientKeyboardBacklightController.AmbientKeyboardBacklightListener { }
+        ambientController.registerAmbientBacklightListener(ambientListener1)
+        assertEquals(
+            "Should register a new sensor listener", 1, listenerRegistrationCount
+        )
+        assertTrue("Should have sensor listener registered", listenerRegistered)
+
+        val ambientListener2 =
+            AmbientKeyboardBacklightController.AmbientKeyboardBacklightListener { }
+        ambientController.registerAmbientBacklightListener(ambientListener2)
+        assertEquals(
+            "Should not register a new sensor listener when adding a second ambient listener",
+            1,
+            listenerRegistrationCount
+        )
+        assertTrue("Should have sensor listener registered", listenerRegistered)
+
+        ambientController.unregisterAmbientBacklightListener(ambientListener1)
+        assertTrue("Should have sensor listener registered", listenerRegistered)
+
+        ambientController.unregisterAmbientBacklightListener(ambientListener2)
+        assertFalse(
+            "Should not have sensor listener registered if there are no ambient listeners",
+            listenerRegistered
+        )
+    }
+
+    @Test
+    fun testDisplayChange_shouldNotReRegisterListener_ifUniqueIdSame() {
+        setupSensorWithInitialLux(0F)
+
+        val count = listenerRegistrationCount
+        ambientController.onDisplayChanged(Display.DEFAULT_DISPLAY)
+        testLooper.dispatchAll()
+
+        assertEquals(
+            "Should not re-register listener on display change if unique is same",
+            count,
+            listenerRegistrationCount
+        )
+    }
+
+    @Test
+    fun testDisplayChange_shouldReRegisterListener_ifUniqueIdChanges() {
+        setupSensorWithInitialLux(0F)
+
+        val count = listenerRegistrationCount
+        currentDisplayInfo.uniqueId = "xyz"
+        ambientController.onDisplayChanged(Display.DEFAULT_DISPLAY)
+        testLooper.dispatchAll()
+
+        assertEquals(
+            "Should re-register listener on display change if unique id changed",
+            count + 1,
+            listenerRegistrationCount
+        )
+    }
+
+    @Test
+    fun testBrightnessDoesntChange_betweenIncreaseAndDecreaseThresholds() {
+        setupSensorWithInitialLux(1001F)
+
+        // Previous state: Step 1 [value = 100, increaseThreshold = 1000, decreaseThreshold = -1]
+        // Current state: Step 2 [value = 200, increaseThreshold = 2000, decreaseThreshold = 900]
+        lastBrightnessCallback = -1
+        repeat(HYSTERESIS_THRESHOLD) {
+            sendAmbientLuxValue(999F)
+        }
+        testLooper.dispatchAll()
+
+        assertEquals(
+            "Should not receive any callback for brightness change",
+            -1,
+            lastBrightnessCallback
+        )
+    }
+
+    @Test
+    fun testBrightnessDoesntChange_onChangeOccurringLessThanHysteresisThreshold() {
+        setupSensorWithInitialLux(1001F)
+
+        // Previous state: Step 1 [value = 100, increaseThreshold = 1000, decreaseThreshold = -1]
+        // Current state: Step 2 [value = 200, increaseThreshold = 2000, decreaseThreshold = 900]
+        lastBrightnessCallback = -1
+        repeat(HYSTERESIS_THRESHOLD - 1) {
+            sendAmbientLuxValue(2001F)
+        }
+        testLooper.dispatchAll()
+
+        assertEquals(
+            "Should not receive any callback for brightness change",
+            -1,
+            lastBrightnessCallback
+        )
+    }
+
+    private fun sendAmbientLuxValue(luxValue: Float) {
+        ambientController.onSensorChanged(SensorEvent(lightSensor, 0, 0, floatArrayOf(luxValue)))
+    }
+}
diff --git a/services/tests/servicestests/src/com/android/server/input/KeyboardBacklightControllerTests.kt b/services/tests/servicestests/src/com/android/server/input/KeyboardBacklightControllerTests.kt
index ef15ccba4c746..67158f24839dc 100644
--- a/services/tests/servicestests/src/com/android/server/input/KeyboardBacklightControllerTests.kt
+++ b/services/tests/servicestests/src/com/android/server/input/KeyboardBacklightControllerTests.kt
@@ -37,6 +37,8 @@ import com.android.server.input.KeyboardBacklightController.MAX_BRIGHTNESS_CHANG
 import com.android.server.input.KeyboardBacklightController.USER_INACTIVITY_THRESHOLD_MILLIS
 import org.junit.After
 import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNotEquals
 import org.junit.Assert.assertNotNull
 import org.junit.Assert.assertNull
 import org.junit.Assert.assertTrue
@@ -154,7 +156,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklightIncrementDecrement() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
@@ -168,7 +174,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardWithoutBacklight() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithoutBacklight = createKeyboard(DEVICE_ID)
             val keyboardInputLight = createLight(LIGHT_ID, Light.LIGHT_TYPE_INPUT)
             `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithoutBacklight)
@@ -182,7 +192,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardWithMultipleLight() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             val keyboardInputLight = createLight(SECOND_LIGHT_ID, Light.LIGHT_TYPE_INPUT)
@@ -204,7 +218,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testRestoreBacklightOnInputDeviceAdded() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
@@ -233,7 +251,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testRestoreBacklightOnInputDeviceChanged() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
@@ -265,7 +287,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklight_registerUnregisterListener() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             val maxLevel = DEFAULT_BRIGHTNESS_VALUE_FOR_LEVEL.size - 1
@@ -314,7 +340,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklight_userActivity() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
@@ -346,7 +376,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklight_displayOnOff() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
@@ -436,7 +470,11 @@ class KeyboardBacklightControllerTests {
     @Test
     @UiThreadTest
     fun testKeyboardBacklightAnimation_onChangeLevels() {
-        KeyboardBacklightFlags(animationEnabled = true, customLevelsEnabled = false).use {
+        KeyboardBacklightFlags(
+            animationEnabled = true,
+            customLevelsEnabled = false,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
             `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
@@ -459,7 +497,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklightPreferredLevels() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = true).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = true,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val suggestedLevels = intArrayOf(0, 22, 63, 135, 196, 255)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT,
@@ -475,7 +517,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklightPreferredLevels_moreThanMax_shouldUseDefault() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = true).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = true,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val suggestedLevels = IntArray(MAX_BRIGHTNESS_CHANGE_STEPS + 1) { 10 * (it + 1) }
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT,
@@ -491,7 +537,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklightPreferredLevels_mustHaveZeroAndMaxBrightnessAsBounds() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = true).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = true,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val suggestedLevels = intArrayOf(22, 63, 135, 196)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT,
@@ -508,7 +558,11 @@ class KeyboardBacklightControllerTests {
 
     @Test
     fun testKeyboardBacklightPreferredLevels_dropsOutOfBoundsLevels() {
-        KeyboardBacklightFlags(animationEnabled = false, customLevelsEnabled = true).use {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = true,
+            ambientControlEnabled = false
+        ).use {
             val keyboardWithBacklight = createKeyboard(DEVICE_ID)
             val suggestedLevels = intArrayOf(22, 63, 135, 400, 196, 1000)
             val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT,
@@ -523,10 +577,148 @@ class KeyboardBacklightControllerTests {
         }
     }
 
+    @Test
+    fun testAmbientBacklightControl_doesntRestoreBacklightLevel() {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = true
+        ).use {
+            val keyboardWithBacklight = createKeyboard(DEVICE_ID)
+            val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
+            `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
+            `when`(iInputManager.getLights(DEVICE_ID)).thenReturn(listOf(keyboardBacklight))
+
+            dataStore.setKeyboardBacklightBrightness(
+                keyboardWithBacklight.descriptor,
+                LIGHT_ID,
+                DEFAULT_BRIGHTNESS_VALUE_FOR_LEVEL[1]
+            )
+
+            keyboardBacklightController.onInputDeviceAdded(DEVICE_ID)
+            keyboardBacklightController.notifyUserActivity()
+            testLooper.dispatchNext()
+            assertNull(
+                "Keyboard backlight level should not be restored to the saved level",
+                lightColorMap[LIGHT_ID]
+            )
+        }
+    }
+
+    @Test
+    fun testAmbientBacklightControl_doesntBackupBacklightLevel() {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = true
+        ).use {
+            val keyboardWithBacklight = createKeyboard(DEVICE_ID)
+            val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
+            `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
+            `when`(iInputManager.getLights(DEVICE_ID)).thenReturn(listOf(keyboardBacklight))
+
+            keyboardBacklightController.onInputDeviceAdded(DEVICE_ID)
+            incrementKeyboardBacklight(DEVICE_ID)
+            assertFalse(
+                "Light value should not be backed up if ambient control is enabled",
+                dataStore.getKeyboardBacklightBrightness(
+                    keyboardWithBacklight.descriptor, LIGHT_ID
+                ).isPresent
+            )
+        }
+    }
+
+    @Test
+    fun testAmbientBacklightControl_incrementLevel_afterAmbientChange() {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = true
+        ).use {
+            val keyboardWithBacklight = createKeyboard(DEVICE_ID)
+            val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
+            `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
+            `when`(iInputManager.getLights(DEVICE_ID)).thenReturn(listOf(keyboardBacklight))
+            keyboardBacklightController.onInputDeviceAdded(DEVICE_ID)
+            sendAmbientBacklightValue(1)
+            assertEquals(
+                "Light value should be changed to ambient provided value",
+                Color.argb(1, 0, 0, 0),
+                lightColorMap[LIGHT_ID]
+            )
+
+            incrementKeyboardBacklight(DEVICE_ID)
+
+            assertEquals(
+                "Light value for level after increment post Ambient change is mismatched",
+                Color.argb(DEFAULT_BRIGHTNESS_VALUE_FOR_LEVEL[1], 0, 0, 0),
+                lightColorMap[LIGHT_ID]
+            )
+        }
+    }
+
+    @Test
+    fun testAmbientBacklightControl_decrementLevel_afterAmbientChange() {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = true
+        ).use {
+            val keyboardWithBacklight = createKeyboard(DEVICE_ID)
+            val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
+            `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
+            `when`(iInputManager.getLights(DEVICE_ID)).thenReturn(listOf(keyboardBacklight))
+            keyboardBacklightController.onInputDeviceAdded(DEVICE_ID)
+            sendAmbientBacklightValue(254)
+            assertEquals(
+                "Light value should be changed to ambient provided value",
+                Color.argb(254, 0, 0, 0),
+                lightColorMap[LIGHT_ID]
+            )
+
+            decrementKeyboardBacklight(DEVICE_ID)
+
+            val numLevels = DEFAULT_BRIGHTNESS_VALUE_FOR_LEVEL.size
+            assertEquals(
+                "Light value for level after decrement post Ambient change is mismatched",
+                Color.argb(DEFAULT_BRIGHTNESS_VALUE_FOR_LEVEL[numLevels - 2], 0, 0, 0),
+                lightColorMap[LIGHT_ID]
+            )
+        }
+    }
+
+    @Test
+    fun testAmbientBacklightControl_ambientChanges_afterManualChange() {
+        KeyboardBacklightFlags(
+            animationEnabled = false,
+            customLevelsEnabled = false,
+            ambientControlEnabled = true
+        ).use {
+            val keyboardWithBacklight = createKeyboard(DEVICE_ID)
+            val keyboardBacklight = createLight(LIGHT_ID, Light.LIGHT_TYPE_KEYBOARD_BACKLIGHT)
+            `when`(iInputManager.getInputDevice(DEVICE_ID)).thenReturn(keyboardWithBacklight)
+            `when`(iInputManager.getLights(DEVICE_ID)).thenReturn(listOf(keyboardBacklight))
+            keyboardBacklightController.onInputDeviceAdded(DEVICE_ID)
+            incrementKeyboardBacklight(DEVICE_ID)
+            assertEquals(
+                "Light value should be changed to the first level",
+                Color.argb(DEFAULT_BRIGHTNESS_VALUE_FOR_LEVEL[1], 0, 0, 0),
+                lightColorMap[LIGHT_ID]
+            )
+
+            sendAmbientBacklightValue(100)
+            assertNotEquals(
+                "Light value should not change based on ambient changes after manual changes",
+                Color.argb(100, 0, 0, 0),
+                lightColorMap[LIGHT_ID]
+            )
+        }
+    }
+
     private fun assertIncrementDecrementForLevels(
-            device: InputDevice,
-            light: Light,
-            expectedLevels: IntArray
+        device: InputDevice,
+        light: Light,
+        expectedLevels: IntArray
     ) {
         val deviceId = device.id
         val lightId = light.id
@@ -612,6 +804,12 @@ class KeyboardBacklightControllerTests {
         testLooper.dispatchAll()
     }
 
+    private fun sendAmbientBacklightValue(brightnessValue: Int) {
+        keyboardBacklightController.handleAmbientLightValueChanged(brightnessValue)
+        keyboardBacklightController.notifyUserActivity()
+        testLooper.dispatchAll()
+    }
+
     class KeyboardBacklightState(
         val deviceId: Int,
         val brightnessLevel: Int,
@@ -620,12 +818,15 @@ class KeyboardBacklightControllerTests {
     )
 
     private inner class KeyboardBacklightFlags constructor(
-            animationEnabled: Boolean,
-            customLevelsEnabled: Boolean
+        animationEnabled: Boolean,
+        customLevelsEnabled: Boolean,
+        ambientControlEnabled: Boolean
     ) : AutoCloseable {
         init {
             InputFeatureFlagProvider.setKeyboardBacklightAnimationEnabled(animationEnabled)
             InputFeatureFlagProvider.setKeyboardBacklightCustomLevelsEnabled(customLevelsEnabled)
+            InputFeatureFlagProvider
+                .setAmbientKeyboardBacklightControlEnabled(ambientControlEnabled)
         }
 
         override fun close() {