Merge "Add sensor for flip to screen off. See go/flip-to-screen-off-design-doc for design details." into sc-dev

services/core/java/com/android/server/power/FaceDownDetector.java

@@ -0,0 +1,456 @@
+/*
+ * Copyright (C) 2021 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.power;
+
+import static android.provider.DeviceConfig.NAMESPACE_ATTENTION_MANAGER_SERVICE;
+
+import android.annotation.NonNull;
+import android.app.ActivityThread;
+import android.content.BroadcastReceiver;
+import android.content.Context;
+import android.content.Intent;
+import android.content.IntentFilter;
+import android.hardware.Sensor;
+import android.hardware.SensorEvent;
+import android.hardware.SensorEventListener;
+import android.hardware.SensorManager;
+import android.os.Handler;
+import android.os.Looper;
+import android.os.SystemClock;
+import android.provider.DeviceConfig;
+import android.util.Slog;
+
+import com.android.internal.util.FrameworkStatsLog;
+
+import java.io.PrintWriter;
+import java.time.Duration;
+import java.util.Objects;
+import java.util.Set;
+import java.util.function.Consumer;
+
+/**
+ * Class used to detect when the phone is placed face down. This is used for Flip to Screen Off. A
+ * client can use this detector to trigger state changes like screen off when the phone is face
+ * down.
+ */
+public class FaceDownDetector implements SensorEventListener {
+
+    private static final String TAG = "FaceDownDetector";
+    private static final boolean DEBUG = false;
+
+    private static final int SCREEN_OFF_RESULT =
+            FrameworkStatsLog.FACE_DOWN_REPORTED__FACE_DOWN_RESPONSE__SCREEN_OFF;
+    private static final int USER_INTERACTION =
+            FrameworkStatsLog.FACE_DOWN_REPORTED__FACE_DOWN_RESPONSE__USER_INTERACTION;
+    private static final int UNFLIP =
+            FrameworkStatsLog.FACE_DOWN_REPORTED__FACE_DOWN_RESPONSE__UNFLIP;
+
+    /**
+     * Used by the ExponentialMovingAverage accelerations, this determines how quickly the
+     * average can change. A number closer to 1 will mean it will take longer to change.
+     */
+    private static final float MOVING_AVERAGE_WEIGHT = 0.5f;
+
+    /** DeviceConfig flag name, if {@code true}, enables Face Down features. */
+    private static final String KEY_FEATURE_ENABLED = "enable_flip_to_screen_off";
+
+    /** Default value in absence of {@link DeviceConfig} override. */
+    private static final boolean DEFAULT_FEATURE_ENABLED = true;
+
+    private boolean mIsEnabled;
+
+    /**
+     * DeviceConfig flag name, determines how long to disable sensor when user interacts while
+     * device is flipped.
+     */
+    private static final String KEY_INTERACTION_BACKOFF = "face_down_interaction_backoff_millis";
+
+    /** Default value in absence of {@link DeviceConfig} override. */
+    private static final long DEFAULT_INTERACTION_BACKOFF = 60_000;
+
+    private long mUserInteractionBackoffMillis;
+
+    /**
+     * DeviceConfig flag name, defines the max change in acceleration which will prevent face down
+     * due to movement.
+     */
+    static final String KEY_ACCELERATION_THRESHOLD = "acceleration_threshold";
+
+    /** Default value in absence of {@link DeviceConfig} override. */
+    static final float DEFAULT_ACCELERATION_THRESHOLD = 0.2f;
+
+    private float mAccelerationThreshold;
+
+    /**
+     * DeviceConfig flag name, defines the maximum z-axis acceleration that will indicate the phone
+     * is face down.
+     */
+    static final String KEY_Z_ACCELERATION_THRESHOLD = "z_acceleration_threshold";
+
+    /** Default value in absence of {@link DeviceConfig} override. */
+    static final float DEFAULT_Z_ACCELERATION_THRESHOLD = -9.5f;
+
+    private float mZAccelerationThreshold;
+
+    /**
+     * After going face down, we relax the threshold to make it more difficult to exit face down
+     * than to enter it.
+     */
+    private float mZAccelerationThresholdLenient;
+
+    /**
+     * DeviceConfig flag name, defines the minimum amount of time that has to pass while the phone
+     * is face down and not moving in order to trigger face down behavior, in milliseconds.
+     */
+    static final String KEY_TIME_THRESHOLD_MILLIS = "time_threshold_millis";
+
+    /** Default value in absence of {@link DeviceConfig} override. */
+    static final long DEFAULT_TIME_THRESHOLD_MILLIS = 1_000L;
+
+    private Duration mTimeThreshold;
+
+    private Sensor mAccelerometer;
+    private SensorManager mSensorManager;
+    private final Consumer<Boolean> mOnFlip;
+
+    /** Values we store for logging purposes. */
+    private long mLastFlipTime = 0L;
+    public int mPreviousResultType = 0;
+    public long mPreviousResultTime = 0L;
+    private long mMillisSaved = 0L;
+
+    private final ExponentialMovingAverage mCurrentXYAcceleration =
+            new ExponentialMovingAverage(MOVING_AVERAGE_WEIGHT);
+    private final ExponentialMovingAverage mCurrentZAcceleration =
+            new ExponentialMovingAverage(MOVING_AVERAGE_WEIGHT);
+
+    private boolean mFaceDown = false;
+    private boolean mActive = false;
+
+    private float mPrevAcceleration = 0;
+    private long mPrevAccelerationTime = 0;
+
+    private boolean mZAccelerationIsFaceDown = false;
+    private long mZAccelerationFaceDownTime = 0L;
+
+    private final Handler mHandler;
+    private final Runnable mUserActivityRunnable;
+
+    public FaceDownDetector(@NonNull Consumer<Boolean> onFlip) {
+        mOnFlip = Objects.requireNonNull(onFlip);
+        mHandler = new Handler(Looper.getMainLooper());
+        mUserActivityRunnable = () -> {
+            if (mFaceDown) {
+                exitFaceDown(USER_INTERACTION, SystemClock.uptimeMillis() - mLastFlipTime);
+                checkAndUpdateActiveState(false);
+            }
+        };
+    }
+
+    /** Initializes the FaceDownDetector and all necessary listeners. */
+    public void systemReady(Context context) {
+        mSensorManager = context.getSystemService(SensorManager.class);
+        mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
+        readValuesFromDeviceConfig();
+        checkAndUpdateActiveState(true);
+        DeviceConfig.addOnPropertiesChangedListener(NAMESPACE_ATTENTION_MANAGER_SERVICE,
+                ActivityThread.currentApplication().getMainExecutor(),
+                (properties) -> onDeviceConfigChange(properties.getKeyset()));
+        IntentFilter intentFilter = new IntentFilter();
+        intentFilter.addAction(Intent.ACTION_SCREEN_OFF);
+        intentFilter.addAction(Intent.ACTION_SCREEN_ON);
+        intentFilter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY);
+        context.registerReceiver(new ScreenStateReceiver(), intentFilter);
+    }
+
+    /**
+     * Sets the active state of the detector. If false, we will not process accelerometer changes.
+     */
+    private void checkAndUpdateActiveState(boolean active) {
+        if (mIsEnabled && mActive != active) {
+            final long currentTime = SystemClock.uptimeMillis();
+            // Don't make active if there was recently a user interaction while face down.
+            if (active && mPreviousResultType == USER_INTERACTION
+                    && currentTime - mPreviousResultTime  < mUserInteractionBackoffMillis) {
+                return;
+            }
+            if (DEBUG) Slog.d(TAG, "Update active - " + active);
+            mActive = active;
+            if (!active) {
+                if (mFaceDown && mPreviousResultTime != USER_INTERACTION) {
+                    mPreviousResultType = SCREEN_OFF_RESULT;
+                    mPreviousResultTime = currentTime;
+                }
+                mSensorManager.unregisterListener(this);
+                mFaceDown = false;
+                mOnFlip.accept(false);
+            } else {
+                if (mPreviousResultType == SCREEN_OFF_RESULT) {
+                    logScreenOff();
+                }
+                mSensorManager.registerListener(
+                        this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
+            }
+        }
+    }
+
+    /** Prints state information about FaceDownDetector */
+    public void dump(PrintWriter pw) {
+        pw.println("FaceDownDetector:");
+        pw.println("  mFaceDown=" + mFaceDown);
+        pw.println("  mActive=" + mActive);
+        pw.println("  mLastFlipTime=" + mLastFlipTime);
+        pw.println("  mUserInteractionBackoffMillis=" + mUserInteractionBackoffMillis);
+        pw.println("  mPreviousResultTime=" + mPreviousResultTime);
+        pw.println("  mPreviousResultType=" + mPreviousResultType);
+        pw.println("  mMillisSaved=" + mMillisSaved);
+        pw.println("  mZAccelerationThreshold=" + mZAccelerationThreshold);
+        pw.println("  mAccelerationThreshold=" + mAccelerationThreshold);
+        pw.println("  mTimeThreshold=" + mTimeThreshold);
+    }
+
+    @Override
+    public void onSensorChanged(SensorEvent event) {
+        if (event.sensor.getType() != Sensor.TYPE_ACCELEROMETER) return;
+        if (!mActive || !mIsEnabled) return;
+
+        final float x = event.values[0];
+        final float y = event.values[1];
+        mCurrentXYAcceleration.updateMovingAverage(x * x + y * y);
+        mCurrentZAcceleration.updateMovingAverage(event.values[2]);
+
+        // Detect movement
+        // If the x, y acceleration is within the acc threshold for at least a length of time longer
+        // than the time threshold, we set moving to true.
+        final long curTime = event.timestamp;
+        if (Math.abs(mCurrentXYAcceleration.mMovingAverage - mPrevAcceleration)
+                > mAccelerationThreshold) {
+            mPrevAcceleration = mCurrentXYAcceleration.mMovingAverage;
+            mPrevAccelerationTime = curTime;
+        }
+        final boolean moving = curTime - mPrevAccelerationTime <= mTimeThreshold.toNanos();
+
+        // If the z acceleration is beyond the gravity/z-acceleration threshold for at least a
+        // length of time longer than the time threshold, we set isFaceDownForPeriod to true.
+        final float zAccelerationThreshold =
+                mFaceDown ? mZAccelerationThresholdLenient : mZAccelerationThreshold;
+        final boolean isCurrentlyFaceDown =
+                mCurrentZAcceleration.mMovingAverage < zAccelerationThreshold;
+        final boolean isFaceDownForPeriod = isCurrentlyFaceDown
+                && mZAccelerationIsFaceDown
+                && curTime - mZAccelerationFaceDownTime > mTimeThreshold.toNanos();
+        if (isCurrentlyFaceDown && !mZAccelerationIsFaceDown) {
+            mZAccelerationFaceDownTime = curTime;
+            mZAccelerationIsFaceDown = true;
+        } else if (!isCurrentlyFaceDown) {
+            mZAccelerationIsFaceDown = false;
+        }
+
+
+        if (!moving && isFaceDownForPeriod && !mFaceDown) {
+            faceDownDetected();
+        } else if (!isFaceDownForPeriod && mFaceDown) {
+            unFlipDetected();
+        }
+    }
+
+    @Override
+    public void onAccuracyChanged(Sensor sensor, int accuracy) {}
+
+    private void faceDownDetected() {
+        if (DEBUG) Slog.d(TAG, "Triggered faceDownDetected.");
+        mLastFlipTime = SystemClock.uptimeMillis();
+        mFaceDown = true;
+        mOnFlip.accept(true);
+    }
+
+    private void unFlipDetected() {
+        if (DEBUG) Slog.d(TAG, "Triggered exitFaceDown");
+        exitFaceDown(UNFLIP, SystemClock.uptimeMillis() - mLastFlipTime);
+    }
+
+    /**
+     * The user interacted with the screen while face down, indicated the phone is in use.
+     * We log this event and temporarily make this detector inactive.
+     */
+    public void userActivity() {
+        mHandler.post(mUserActivityRunnable);
+    }
+
+    private void exitFaceDown(int resultType, long millisSinceFlip) {
+        FrameworkStatsLog.write(FrameworkStatsLog.FACE_DOWN_REPORTED,
+                resultType,
+                millisSinceFlip,
+                /* millis_until_normal_timeout= */ 0L,
+                /* millis_until_next_screen_on= */ 0L);
+        mFaceDown = false;
+        mLastFlipTime = 0L;
+        mPreviousResultType = resultType;
+        mPreviousResultTime = SystemClock.uptimeMillis();
+        mOnFlip.accept(false);
+    }
+
+    private void logScreenOff() {
+        if (mPreviousResultType == SCREEN_OFF_RESULT) {
+            final long currentTime = SystemClock.uptimeMillis();
+            FrameworkStatsLog.write(FrameworkStatsLog.FACE_DOWN_REPORTED,
+                    mPreviousResultType,
+                    /* millis_since_flip= */ mPreviousResultTime  - mLastFlipTime,
+                    mMillisSaved,
+                    /* millis_until_next_screen_on= */ currentTime - mPreviousResultTime);
+            mPreviousResultType = -1;
+        }
+    }
+
+    private boolean isEnabled() {
+        return DeviceConfig.getBoolean(NAMESPACE_ATTENTION_MANAGER_SERVICE, KEY_FEATURE_ENABLED,
+                DEFAULT_FEATURE_ENABLED);
+    }
+
+    private float getAccelerationThreshold() {
+        return getFloatFlagValue(KEY_ACCELERATION_THRESHOLD,
+                DEFAULT_ACCELERATION_THRESHOLD,
+                -2.0f,
+                2.0f);
+    }
+
+    private float getZAccelerationThreshold() {
+        return getFloatFlagValue(KEY_Z_ACCELERATION_THRESHOLD,
+                DEFAULT_Z_ACCELERATION_THRESHOLD,
+                -15.0f,
+                0.0f);
+    }
+
+    private long getUserInteractionBackoffMillis() {
+        return getLongFlagValue(KEY_INTERACTION_BACKOFF,
+                DEFAULT_INTERACTION_BACKOFF,
+                0,
+                3600_000);
+    }
+
+    private float getFloatFlagValue(String key, float defaultValue, float min, float max) {
+        final float value = DeviceConfig.getFloat(NAMESPACE_ATTENTION_MANAGER_SERVICE,
+                key,
+                defaultValue);
+
+        if (value < min || value > max) {
+            Slog.w(TAG, "Bad flag value supplied for: " + key);
+            return defaultValue;
+        }
+
+        return value;
+    }
+
+    private long getLongFlagValue(String key, long defaultValue, long min, long max) {
+        final long value = DeviceConfig.getLong(NAMESPACE_ATTENTION_MANAGER_SERVICE,
+                key,
+                defaultValue);
+
+        if (value < min || value > max) {
+            Slog.w(TAG, "Bad flag value supplied for: " + key);
+            return defaultValue;
+        }
+
+        return value;
+    }
+
+    private Duration getTimeThreshold() {
+        final long millis = DeviceConfig.getLong(NAMESPACE_ATTENTION_MANAGER_SERVICE,
+                KEY_TIME_THRESHOLD_MILLIS,
+                DEFAULT_TIME_THRESHOLD_MILLIS);
+
+        if (millis < 0 || millis > 15_000) {
+            Slog.w(TAG, "Bad flag value supplied for: " + KEY_TIME_THRESHOLD_MILLIS);
+            return Duration.ofMillis(DEFAULT_TIME_THRESHOLD_MILLIS);
+        }
+
+        return Duration.ofMillis(millis);
+    }
+
+    private void onDeviceConfigChange(@NonNull Set<String> keys) {
+        for (String key : keys) {
+            switch (key) {
+                case KEY_ACCELERATION_THRESHOLD:
+                case KEY_Z_ACCELERATION_THRESHOLD:
+                case KEY_TIME_THRESHOLD_MILLIS:
+                case KEY_FEATURE_ENABLED:
+                    readValuesFromDeviceConfig();
+                    return;
+                default:
+                    Slog.i(TAG, "Ignoring change on " + key);
+            }
+        }
+    }
+
+    private void readValuesFromDeviceConfig() {
+        mAccelerationThreshold = getAccelerationThreshold();
+        mZAccelerationThreshold = getZAccelerationThreshold();
+        mZAccelerationThresholdLenient = mZAccelerationThreshold + 1.0f;
+        mTimeThreshold = getTimeThreshold();
+        mIsEnabled = isEnabled();
+        mUserInteractionBackoffMillis = getUserInteractionBackoffMillis();
+
+        Slog.i(TAG, "readValuesFromDeviceConfig():"
+                + "\nmAccelerationThreshold=" + mAccelerationThreshold
+                + "\nmZAccelerationThreshold=" + mZAccelerationThreshold
+                + "\nmTimeThreshold=" + mTimeThreshold
+                + "\nmIsEnabled=" + mIsEnabled);
+    }
+
+    /**
+     * Sets how much screen on time might be saved as a result of this detector. Currently used for
+     * logging purposes.
+     */
+    public void setMillisSaved(long millisSaved) {
+        mMillisSaved = millisSaved;
+    }
+
+    private final class ScreenStateReceiver extends BroadcastReceiver {
+        @Override
+        public void onReceive(Context context, Intent intent) {
+            if (Intent.ACTION_SCREEN_OFF.equals(intent.getAction())) {
+                checkAndUpdateActiveState(false);
+            } else if (Intent.ACTION_SCREEN_ON.equals(intent.getAction())) {
+                checkAndUpdateActiveState(true);
+            }
+        }
+    }
+
+    private final class ExponentialMovingAverage {
+        private final float mAlpha;
+        private final float mInitialAverage;
+        private float mMovingAverage;
+
+        ExponentialMovingAverage(float alpha) {
+            this(alpha, 0.0f);
+        }
+
+        ExponentialMovingAverage(float alpha, float initialAverage) {
+            this.mAlpha = alpha;
+            this.mInitialAverage = initialAverage;
+            this.mMovingAverage = initialAverage;
+        }
+
+        void updateMovingAverage(float newValue) {
+            mMovingAverage = newValue + mAlpha * (mMovingAverage - newValue);
+        }
+
+        void reset() {
+            mMovingAverage = this.mInitialAverage;
+        }
+    }
+}

services/core/java/com/android/server/power/Notifier.java

@@ -119,6 +119,7 @@ public class Notifier {
     private final AppOpsManager mAppOps;
     private final SuspendBlocker mSuspendBlocker;
     private final WindowManagerPolicy mPolicy;
+    private final FaceDownDetector mFaceDownDetector;
     private final ActivityManagerInternal mActivityManagerInternal;
     private final InputManagerInternal mInputManagerInternal;
     private final InputMethodManagerInternal mInputMethodManagerInternal;
@@ -165,12 +166,14 @@ public class Notifier {
     private boolean mUserActivityPending;
 
     public Notifier(Looper looper, Context context, IBatteryStats batteryStats,
-            SuspendBlocker suspendBlocker, WindowManagerPolicy policy) {
+            SuspendBlocker suspendBlocker, WindowManagerPolicy policy,
+            FaceDownDetector faceDownDetector) {
         mContext = context;
         mBatteryStats = batteryStats;
         mAppOps = mContext.getSystemService(AppOpsManager.class);
         mSuspendBlocker = suspendBlocker;
         mPolicy = policy;
+        mFaceDownDetector = faceDownDetector;
         mActivityManagerInternal = LocalServices.getService(ActivityManagerInternal.class);
         mInputManagerInternal = LocalServices.getService(InputManagerInternal.class);
         mInputMethodManagerInternal = LocalServices.getService(InputMethodManagerInternal.class);
@@ -654,6 +657,7 @@ public class Notifier {
         TelephonyManager tm = mContext.getSystemService(TelephonyManager.class);
         tm.notifyUserActivity();
         mPolicy.userActivity();
+        mFaceDownDetector.userActivity();
     }
 
     void postEnhancedDischargePredictionBroadcast(long delayMs) {

services/core/java/com/android/server/power/PowerManagerService.java

@@ -176,6 +176,8 @@ public final class PowerManagerService extends SystemService
     private static final int DIRTY_VR_MODE_CHANGED = 1 << 13;
     // Dirty bit: attentive timer may have timed out
     private static final int DIRTY_ATTENTIVE = 1 << 14;
+    // Dirty bit: phone flipped to face down
+    private static final int DIRTY_FACE_DOWN = 1 << 15;
 
     // Summarizes the state of all active wakelocks.
     private static final int WAKE_LOCK_CPU = 1 << 0;
@@ -263,6 +265,7 @@ public final class PowerManagerService extends SystemService
     private final BatterySaverStateMachine mBatterySaverStateMachine;
     private final BatterySavingStats mBatterySavingStats;
     private final AttentionDetector mAttentionDetector;
+    private final FaceDownDetector mFaceDownDetector;
     private final BinderService mBinderService;
     private final LocalService mLocalService;
     private final NativeWrapper mNativeWrapper;
@@ -547,6 +550,10 @@ public final class PowerManagerService extends SystemService
     public final float mScreenBrightnessMaximumVr;
     public final float mScreenBrightnessDefaultVr;
 
+    // Value we store for tracking face down behavior.
+    private boolean mIsFaceDown = false;
+    private long mLastFlipTime = 0L;
+
     // The screen brightness mode.
     // One of the Settings.System.SCREEN_BRIGHTNESS_MODE_* constants.
     private int mScreenBrightnessModeSetting;
@@ -791,8 +798,10 @@ public final class PowerManagerService extends SystemService
     @VisibleForTesting
     static class Injector {
         Notifier createNotifier(Looper looper, Context context, IBatteryStats batteryStats,
-                SuspendBlocker suspendBlocker, WindowManagerPolicy policy) {
-            return new Notifier(looper, context, batteryStats, suspendBlocker, policy);
+                SuspendBlocker suspendBlocker, WindowManagerPolicy policy,
+                FaceDownDetector faceDownDetector) {
+            return new Notifier(
+                    looper, context, batteryStats, suspendBlocker, policy, faceDownDetector);
         }
 
         SuspendBlocker createSuspendBlocker(PowerManagerService service, String name) {
@@ -906,6 +915,7 @@ public final class PowerManagerService extends SystemService
         mAmbientDisplaySuppressionController =
                 mInjector.createAmbientDisplaySuppressionController(context);
         mAttentionDetector = new AttentionDetector(this::onUserAttention, mLock);
+        mFaceDownDetector = new FaceDownDetector(this::onFlip);
 
         mBatterySavingStats = new BatterySavingStats(mLock);
         mBatterySaverPolicy =
@@ -1011,6 +1021,26 @@ public final class PowerManagerService extends SystemService
         }
     }
 
+    private void onFlip(boolean isFaceDown) {
+        long millisUntilNormalTimeout = 0;
+        synchronized (mLock) {
+            mIsFaceDown = isFaceDown;
+            if (isFaceDown) {
+                final long currentTime = mClock.uptimeMillis();
+                mLastFlipTime = currentTime;
+                final long sleepTimeout = getSleepTimeoutLocked(-1L);
+                final long screenOffTimeout = getScreenOffTimeoutLocked(sleepTimeout, -1L);
+                millisUntilNormalTimeout =
+                        mLastUserActivityTime + screenOffTimeout - mClock.uptimeMillis();
+                mDirty |= DIRTY_FACE_DOWN;
+                updatePowerStateLocked();
+            }
+        }
+        if (isFaceDown) {
+            mFaceDownDetector.setMillisSaved(millisUntilNormalTimeout);
+        }
+    }
+
     @Override
     public void onStart() {
         publishBinderService(Context.POWER_SERVICE, mBinderService, /* allowIsolated= */ false,
@@ -1065,7 +1095,7 @@ public final class PowerManagerService extends SystemService
             mBatteryStats = BatteryStatsService.getService();
             mNotifier = mInjector.createNotifier(Looper.getMainLooper(), mContext, mBatteryStats,
                     mInjector.createSuspendBlocker(this, "PowerManagerService.Broadcasts"),
-                    mPolicy);
+                    mPolicy, mFaceDownDetector);
 
             mWirelessChargerDetector = mInjector.createWirelessChargerDetector(sensorManager,
                     mInjector.createSuspendBlocker(
@@ -1099,6 +1129,7 @@ public final class PowerManagerService extends SystemService
 
         mBatterySaverController.systemReady();
         mBatterySaverPolicy.systemReady();
+        mFaceDownDetector.systemReady(mContext);
 
         // Register for settings changes.
         resolver.registerContentObserver(Settings.Secure.getUriFor(
@@ -2283,9 +2314,11 @@ public final class PowerManagerService extends SystemService
                     || getWakefulnessLocked() == WAKEFULNESS_DOZING) {
                 final long attentiveTimeout = getAttentiveTimeoutLocked();
                 final long sleepTimeout = getSleepTimeoutLocked(attentiveTimeout);
-                final long screenOffTimeout = getScreenOffTimeoutLocked(sleepTimeout,
+                long screenOffTimeout = getScreenOffTimeoutLocked(sleepTimeout,
                         attentiveTimeout);
                 final long screenDimDuration = getScreenDimDurationLocked(screenOffTimeout);
+                screenOffTimeout =
+                        getScreenOffTimeoutWithFaceDownLocked(screenOffTimeout, screenDimDuration);
                 final boolean userInactiveOverride = mUserInactiveOverrideFromWindowManager;
                 final long nextProfileTimeout = getNextProfileTimeoutLocked(now);
 
@@ -2541,6 +2574,16 @@ public final class PowerManagerService extends SystemService
                 (long)(screenOffTimeout * mMaximumScreenDimRatioConfig));
     }
 
+    private long getScreenOffTimeoutWithFaceDownLocked(
+            long screenOffTimeout, long screenDimDuration) {
+        // If face down, we decrease the timeout to equal the dim duration so that the
+        // device will go into a dim state.
+        if (mIsFaceDown) {
+            return Math.min(screenDimDuration, screenOffTimeout);
+        }
+        return screenOffTimeout;
+    }
+
     /**
      * Updates the wakefulness of the device.
      *
@@ -3859,6 +3902,8 @@ public final class PowerManagerService extends SystemService
             pw.println("  mDisplayReady=" + mDisplayReady);
             pw.println("  mHoldingWakeLockSuspendBlocker=" + mHoldingWakeLockSuspendBlocker);
             pw.println("  mHoldingDisplaySuspendBlocker=" + mHoldingDisplaySuspendBlocker);
+            pw.println("  mLastFlipTime=" + mLastFlipTime);
+            pw.println("  mIsFaceDown=" + mIsFaceDown);
 
             pw.println();
             pw.println("Settings and Configuration:");
@@ -4003,6 +4048,8 @@ public final class PowerManagerService extends SystemService
             mNotifier.dump(pw);
         }
 
+        mFaceDownDetector.dump(pw);
+
         mAmbientDisplaySuppressionController.dump(pw);
     }
 

services/tests/servicestests/src/com/android/server/power/FaceDownDetectorTest.java

@@ -0,0 +1,165 @@
+/*
+ * Copyright (C) 2021 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.power;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.hardware.Sensor;
+import android.hardware.SensorEvent;
+import android.hardware.SensorManager;
+import android.testing.TestableContext;
+
+import androidx.test.platform.app.InstrumentationRegistry;
+
+import com.android.server.display.TestUtils;
+
+import org.junit.Before;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import java.lang.reflect.Constructor;
+import java.time.Duration;
+
+public class FaceDownDetectorTest {
+    @ClassRule
+    public static final TestableContext sContext = new TestableContext(
+            InstrumentationRegistry.getInstrumentation().getTargetContext(), null);
+
+    private final FaceDownDetector mFaceDownDetector =
+            new FaceDownDetector(this::onFlip);
+
+    @Mock private SensorManager mSensorManager;
+
+    private long mCurrentTime;
+    private int mOnFaceDownCalls = 0;
+    private int mOnFaceDownExitCalls = 0;
+
+    @Before
+    public void setup() {
+        MockitoAnnotations.initMocks(this);
+        sContext.addMockSystemService(SensorManager.class, mSensorManager);
+        mCurrentTime = 0;
+    }
+
+    @Test
+    public void faceDownFor2Seconds_triggersFaceDown() throws Exception {
+        mFaceDownDetector.systemReady(sContext);
+
+        // Face up
+        // Using 0.5 on x to simulate constant acceleration, such as a sloped surface.
+        mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 0.0f, 10.0f));
+
+        for (int i = 0; i < 200; i++) {
+            advanceTime(Duration.ofMillis(20));
+            mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 0.0f, -10.0f));
+        }
+
+        assertThat(mOnFaceDownCalls).isEqualTo(1);
+        assertThat(mOnFaceDownExitCalls).isEqualTo(0);
+    }
+
+    @Test
+    public void faceDownFor2Seconds_withMotion_DoesNotTriggerFaceDown() throws Exception {
+        mFaceDownDetector.systemReady(sContext);
+
+        // Face up
+        mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 0.0f, 10.0f));
+
+        for (int i = 0; i < 100; i++) {
+            advanceTime(Duration.ofMillis(20));
+            //Move along x direction
+            mFaceDownDetector.onSensorChanged(createTestEvent(0.5f * i, 0.0f, -10.0f));
+        }
+
+        assertThat(mOnFaceDownCalls).isEqualTo(0);
+        assertThat(mOnFaceDownExitCalls).isEqualTo(0);
+    }
+
+    @Test
+    public void faceDownForHalfSecond_DoesNotTriggerFaceDown() throws Exception {
+        mFaceDownDetector.systemReady(sContext);
+
+        // Face up
+        mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 0.0f, 10.0f));
+
+        for (int i = 0; i < 100; i++) {
+            advanceTime(Duration.ofMillis(5));
+            mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 0.0f, -10.0f));
+        }
+
+        assertThat(mOnFaceDownCalls).isEqualTo(0);
+        assertThat(mOnFaceDownExitCalls).isEqualTo(0);
+    }
+
+    @Test
+    public void faceDownFor2Seconds_followedByFaceUp_triggersFaceDownExit() throws Exception {
+        mFaceDownDetector.systemReady(sContext);
+
+        // Face up
+        // Using 0.5 on x to simulate constant acceleration, such as a sloped surface.
+        mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 0.0f, 10.0f));
+
+        // Trigger face down
+        for (int i = 0; i < 100; i++) {
+            advanceTime(Duration.ofMillis(20));
+            mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 0.0f, -10.0f));
+        }
+
+        // Phone flips
+        for (int i = 0; i < 10; i++) {
+            advanceTime(Duration.ofMillis(5));
+            mFaceDownDetector.onSensorChanged(createTestEvent(0.5f, 1.0f, 0.0f));
+        }
+
+        assertThat(mOnFaceDownCalls).isEqualTo(1);
+        assertThat(mOnFaceDownExitCalls).isEqualTo(1);
+    }
+
+    private void advanceTime(Duration duration) {
+        mCurrentTime += duration.toNanos();
+    }
+
+    /**
+     * Create a test event to replicate an accelerometer sensor event.
+     * @param x Acceleration along the x dimension.
+     * @param y Acceleration along the y dimension.
+     * @param gravity Acceleration along the Z dimension. Relates to
+     */
+    private SensorEvent createTestEvent(float x, float y, float gravity) throws Exception {
+        final Constructor<SensorEvent> constructor =
+                SensorEvent.class.getDeclaredConstructor(int.class);
+        constructor.setAccessible(true);
+        final SensorEvent event = constructor.newInstance(3);
+        event.sensor =
+                TestUtils.createSensor(Sensor.TYPE_ACCELEROMETER, Sensor.STRING_TYPE_ACCELEROMETER);
+        event.values[0] = x;
+        event.values[1] = y;
+        event.values[2] = gravity;
+        event.timestamp = mCurrentTime;
+        return event;
+    }
+
+    private void onFlip(boolean isFaceDown) {
+        if (isFaceDown) {
+            mOnFaceDownCalls++;
+        } else {
+            mOnFaceDownExitCalls++;
+        }
+    }
+}

services/tests/servicestests/src/com/android/server/power/NotifierTest.java

@@ -209,7 +209,8 @@ public class NotifierTest {
     private final PowerManagerService.Injector mInjector = new PowerManagerService.Injector() {
         @Override
         Notifier createNotifier(Looper looper, Context context, IBatteryStats batteryStats,
-                SuspendBlocker suspendBlocker, WindowManagerPolicy policy) {
+                SuspendBlocker suspendBlocker, WindowManagerPolicy policy,
+                FaceDownDetector faceDownDetector) {
             return mNotifierMock;
         }
 
@@ -296,6 +297,7 @@ public class NotifierTest {
                 IBatteryStats.Stub.asInterface(ServiceManager.getService(
                         BatteryStats.SERVICE_NAME)),
                 mInjector.createSuspendBlocker(mService, "testBlocker"),
+                null,
                 null);
     }
 }

services/tests/servicestests/src/com/android/server/power/PowerManagerServiceTest.java

@@ -211,7 +211,8 @@ public class PowerManagerServiceTest {
         mService = new PowerManagerService(mContextSpy, new Injector() {
             @Override
             Notifier createNotifier(Looper looper, Context context, IBatteryStats batteryStats,
-                    SuspendBlocker suspendBlocker, WindowManagerPolicy policy) {
+                    SuspendBlocker suspendBlocker, WindowManagerPolicy policy,
+                    FaceDownDetector faceDownDetector) {
                 return mNotifierMock;
             }