diff --git a/camera/camera2/ICameraDeviceCallbacks.cpp b/camera/camera2/ICameraDeviceCallbacks.cpp
index 4cc7b5d..f599879 100644
--- a/camera/camera2/ICameraDeviceCallbacks.cpp
+++ b/camera/camera2/ICameraDeviceCallbacks.cpp
@@ -37,6 +37,7 @@
     CAMERA_IDLE,
     CAPTURE_STARTED,
     RESULT_RECEIVED,
+    PREPARED
 };
 
 class BpCameraDeviceCallbacks: public BpInterface<ICameraDeviceCallbacks>
@@ -80,7 +81,6 @@
         data.writeNoException();
     }
 
-
     void onResultReceived(const CameraMetadata& metadata,
             const CaptureResultExtras& resultExtras) {
         ALOGV("onResultReceived");
@@ -93,6 +93,17 @@
         remote()->transact(RESULT_RECEIVED, data, &reply, IBinder::FLAG_ONEWAY);
         data.writeNoException();
     }
+
+    void onPrepared(int streamId)
+    {
+        ALOGV("onPrepared");
+        Parcel data, reply;
+        data.writeInterfaceToken(ICameraDeviceCallbacks::getInterfaceDescriptor());
+        data.writeInt32(streamId);
+        remote()->transact(PREPARED, data, &reply, IBinder::FLAG_ONEWAY);
+        data.writeNoException();
+    }
+
 };
 
 IMPLEMENT_META_INTERFACE(CameraDeviceCallbacks,
@@ -160,6 +171,15 @@
             data.readExceptionCode();
             return NO_ERROR;
         } break;
+        case PREPARED: {
+            ALOGV("onPrepared");
+            CHECK_INTERFACE(ICameraDeviceCallbacks, data, reply);
+            CaptureResultExtras result;
+            int streamId = data.readInt32();
+            onPrepared(streamId);
+            data.readExceptionCode();
+            return NO_ERROR;
+        } break;
         default:
             return BBinder::onTransact(code, data, reply, flags);
     }
diff --git a/camera/camera2/ICameraDeviceUser.cpp b/camera/camera2/ICameraDeviceUser.cpp
index 2ec08a9..9700258 100644
--- a/camera/camera2/ICameraDeviceUser.cpp
+++ b/camera/camera2/ICameraDeviceUser.cpp
@@ -47,7 +47,8 @@
     CREATE_DEFAULT_REQUEST,
     GET_CAMERA_INFO,
     WAIT_UNTIL_IDLE,
-    FLUSH
+    FLUSH,
+    PREPARE
 };
 
 namespace {
@@ -348,6 +349,20 @@
         return res;
     }
 
+    virtual status_t prepare(int streamId)
+    {
+        ALOGV("prepare");
+        Parcel data, reply;
+
+        data.writeInterfaceToken(ICameraDeviceUser::getInterfaceDescriptor());
+        data.writeInt32(streamId);
+
+        remote()->transact(PREPARE, data, &reply);
+
+        reply.readExceptionCode();
+        return reply.readInt32();
+    }
+
 private:
 
 
@@ -545,6 +560,14 @@
             reply->writeInt32(endConfigure());
             return NO_ERROR;
         } break;
+        case PREPARE: {
+            CHECK_INTERFACE(ICameraDeviceUser, data, reply);
+            int streamId = data.readInt32();
+            reply->writeNoException();
+            reply->writeInt32(prepare(streamId));
+            return NO_ERROR;
+        } break;
+
         default:
             return BBinder::onTransact(code, data, reply, flags);
     }
diff --git a/include/camera/camera2/ICameraDeviceCallbacks.h b/include/camera/camera2/ICameraDeviceCallbacks.h
index 670480b..c57b39f 100644
--- a/include/camera/camera2/ICameraDeviceCallbacks.h
+++ b/include/camera/camera2/ICameraDeviceCallbacks.h
@@ -65,6 +65,9 @@
     // One way
     virtual void            onResultReceived(const CameraMetadata& metadata,
                                              const CaptureResultExtras& resultExtras) = 0;
+
+    // One way
+    virtual void            onPrepared(int streamId) = 0;
 };
 
 // ----------------------------------------------------------------------------
diff --git a/include/camera/camera2/ICameraDeviceUser.h b/include/camera/camera2/ICameraDeviceUser.h
index c850924..619b161 100644
--- a/include/camera/camera2/ICameraDeviceUser.h
+++ b/include/camera/camera2/ICameraDeviceUser.h
@@ -133,6 +133,11 @@
      */
     virtual status_t        flush(/*out*/
                                   int64_t* lastFrameNumber = NULL) = 0;
+
+    /**
+     * Preallocate buffers for a given output stream asynchronously.
+     */
+    virtual status_t        prepare(int streamId) = 0;
 };
 
 // ----------------------------------------------------------------------------
diff --git a/services/camera/libcameraservice/api2/CameraDeviceClient.cpp b/services/camera/libcameraservice/api2/CameraDeviceClient.cpp
index 0016174..bf1692d 100644
--- a/services/camera/libcameraservice/api2/CameraDeviceClient.cpp
+++ b/services/camera/libcameraservice/api2/CameraDeviceClient.cpp
@@ -671,6 +671,42 @@
     return mDevice->flush(lastFrameNumber);
 }
 
+status_t CameraDeviceClient::prepare(int streamId) {
+    ATRACE_CALL();
+    ALOGV("%s", __FUNCTION__);
+
+    status_t res = OK;
+    if ( (res = checkPid(__FUNCTION__) ) != OK) return res;
+
+    Mutex::Autolock icl(mBinderSerializationLock);
+
+    // Guard against trying to prepare non-created streams
+    ssize_t index = NAME_NOT_FOUND;
+    for (size_t i = 0; i < mStreamMap.size(); ++i) {
+        if (streamId == mStreamMap.valueAt(i)) {
+            index = i;
+            break;
+        }
+    }
+
+    if (index == NAME_NOT_FOUND) {
+        ALOGW("%s: Camera %d: Invalid stream ID (%d) specified, no stream "
+              "created yet", __FUNCTION__, mCameraId, streamId);
+        return BAD_VALUE;
+    }
+
+    // Also returns BAD_VALUE if stream ID was not valid
+    res = mDevice->prepare(streamId);
+
+    if (res == BAD_VALUE) {
+        ALOGE("%s: Camera %d: Unexpected BAD_VALUE when preparing stream, but we"
+              " already checked and the stream ID (%d) should be valid.",
+              __FUNCTION__, mCameraId, streamId);
+    }
+
+    return res;
+}
+
 status_t CameraDeviceClient::dump(int fd, const Vector<String16>& args) {
     String8 result;
     result.appendFormat("CameraDeviceClient[%d] (%p) dump:\n",
@@ -730,6 +766,14 @@
     }
 }
 
+void CameraDeviceClient::notifyPrepared(int streamId) {
+    // Thread safe. Don't bother locking.
+    sp<ICameraDeviceCallbacks> remoteCb = getRemoteCallback();
+    if (remoteCb != 0) {
+        remoteCb->onPrepared(streamId);
+    }
+}
+
 void CameraDeviceClient::detachDevice() {
     if (mDevice == 0) return;
 
diff --git a/services/camera/libcameraservice/api2/CameraDeviceClient.h b/services/camera/libcameraservice/api2/CameraDeviceClient.h
index f2d8899..b8d8bea 100644
--- a/services/camera/libcameraservice/api2/CameraDeviceClient.h
+++ b/services/camera/libcameraservice/api2/CameraDeviceClient.h
@@ -109,6 +109,9 @@
     virtual status_t      flush(/*out*/
                                 int64_t* lastFrameNumber = NULL);
 
+    // Prepare stream by preallocating its buffers
+    virtual status_t      prepare(int streamId);
+
     /**
      * Interface used by CameraService
      */
@@ -135,6 +138,7 @@
     virtual void notifyError(ICameraDeviceCallbacks::CameraErrorCode errorCode,
                              const CaptureResultExtras& resultExtras);
     virtual void notifyShutter(const CaptureResultExtras& resultExtras, nsecs_t timestamp);
+    virtual void notifyPrepared(int streamId);
 
     /**
      * Interface used by independent components of CameraDeviceClient.
diff --git a/services/camera/libcameraservice/common/Camera2ClientBase.cpp b/services/camera/libcameraservice/common/Camera2ClientBase.cpp
index c0c2314..ba0b264 100644
--- a/services/camera/libcameraservice/common/Camera2ClientBase.cpp
+++ b/services/camera/libcameraservice/common/Camera2ClientBase.cpp
@@ -280,6 +280,14 @@
 }
 
 template <typename TClientBase>
+void Camera2ClientBase<TClientBase>::notifyPrepared(int streamId) {
+    (void)streamId;
+
+    ALOGV("%s: Stream %d now prepared",
+            __FUNCTION__, streamId);
+}
+
+template <typename TClientBase>
 int Camera2ClientBase<TClientBase>::getCameraId() const {
     return TClientBase::mCameraId;
 }
diff --git a/services/camera/libcameraservice/common/Camera2ClientBase.h b/services/camera/libcameraservice/common/Camera2ClientBase.h
index 168ea0a..f1cacdf 100644
--- a/services/camera/libcameraservice/common/Camera2ClientBase.h
+++ b/services/camera/libcameraservice/common/Camera2ClientBase.h
@@ -72,7 +72,7 @@
     virtual void          notifyAutoExposure(uint8_t newState, int triggerId);
     virtual void          notifyAutoWhitebalance(uint8_t newState,
                                                  int triggerId);
-
+    virtual void          notifyPrepared(int streamId);
 
     int                   getCameraId() const;
     const sp<CameraDeviceBase>&
diff --git a/services/camera/libcameraservice/common/CameraDeviceBase.h b/services/camera/libcameraservice/common/CameraDeviceBase.h
index 6ece359..f02fc32 100644
--- a/services/camera/libcameraservice/common/CameraDeviceBase.h
+++ b/services/camera/libcameraservice/common/CameraDeviceBase.h
@@ -199,6 +199,7 @@
         virtual void notifyIdle() = 0;
         virtual void notifyShutter(const CaptureResultExtras &resultExtras,
                 nsecs_t timestamp) = 0;
+        virtual void notifyPrepared(int streamId) = 0;
 
         // Required only for API1
         virtual void notifyAutoFocus(uint8_t newState, int triggerId) = 0;
@@ -281,6 +282,12 @@
     virtual status_t flush(int64_t *lastFrameNumber = NULL) = 0;
 
     /**
+     * Prepare stream by preallocating buffers for it asynchronously.
+     * Calls notifyPrepared() once allocation is complete.
+     */
+    virtual status_t prepare(int streamId) = 0;
+
+    /**
      * Get the HAL device version.
      */
     virtual uint32_t getDeviceVersion() = 0;
diff --git a/services/camera/libcameraservice/device2/Camera2Device.cpp b/services/camera/libcameraservice/device2/Camera2Device.cpp
index 3c5ea9d..f6645f3 100644
--- a/services/camera/libcameraservice/device2/Camera2Device.cpp
+++ b/services/camera/libcameraservice/device2/Camera2Device.cpp
@@ -618,6 +618,12 @@
     return waitUntilDrained();
 }
 
+status_t Camera2Device::prepare(int streamId) {
+    ATRACE_CALL();
+    ALOGE("%s: Camera %d: unimplemented", __FUNCTION__, mId);
+    return NO_INIT;
+}
+
 uint32_t Camera2Device::getDeviceVersion() {
     ATRACE_CALL();
     return mDeviceVersion;
diff --git a/services/camera/libcameraservice/device2/Camera2Device.h b/services/camera/libcameraservice/device2/Camera2Device.h
index 9972606..fd1240a 100644
--- a/services/camera/libcameraservice/device2/Camera2Device.h
+++ b/services/camera/libcameraservice/device2/Camera2Device.h
@@ -84,6 +84,9 @@
             buffer_handle_t *buffer, wp<BufferReleasedListener> listener);
     // Flush implemented as just a wait
     virtual status_t flush(int64_t *lastFrameNumber = NULL);
+    // Prepare is a no-op
+    virtual status_t prepare(int streamId);
+
     virtual uint32_t getDeviceVersion();
     virtual ssize_t getJpegBufferSize(uint32_t width, uint32_t height) const;
 
diff --git a/services/camera/libcameraservice/device3/Camera3Device.cpp b/services/camera/libcameraservice/device3/Camera3Device.cpp
index dc752a6..ec9c70c 100644
--- a/services/camera/libcameraservice/device3/Camera3Device.cpp
+++ b/services/camera/libcameraservice/device3/Camera3Device.cpp
@@ -175,6 +175,8 @@
         return res;
     }
 
+    mPreparerThread = new PreparerThread();
+
     /** Everything is good to go */
 
     mDeviceVersion = device->common.version;
@@ -1190,7 +1192,8 @@
         ALOGW("%s: Replacing old callback listener", __FUNCTION__);
     }
     mListener = listener;
-    mRequestThread->setNotifyCallback(listener);
+    mRequestThread->setNotificationListener(listener);
+    mPreparerThread->setNotificationListener(listener);
 
     return OK;
 }
@@ -1336,6 +1339,34 @@
     return res;
 }
 
+status_t Camera3Device::prepare(int streamId) {
+    ATRACE_CALL();
+    ALOGV("%s: Camera %d: Preparing stream %d", __FUNCTION__, mId, streamId);
+
+    sp<Camera3StreamInterface> stream;
+    ssize_t outputStreamIdx = mOutputStreams.indexOfKey(streamId);
+    if (outputStreamIdx == NAME_NOT_FOUND) {
+        CLOGE("Stream %d does not exist", streamId);
+        return BAD_VALUE;
+    }
+
+    stream = mOutputStreams.editValueAt(outputStreamIdx);
+
+    if (stream->isUnpreparable() || stream->hasOutstandingBuffers() ) {
+        ALOGE("%s: Camera %d: Stream %d has already been a request target",
+                __FUNCTION__, mId, streamId);
+        return BAD_VALUE;
+    }
+
+    if (mRequestThread->isStreamPending(stream)) {
+        ALOGE("%s: Camera %d: Stream %d is already a target in a pending request",
+                __FUNCTION__, mId, streamId);
+        return BAD_VALUE;
+    }
+
+    return mPreparerThread->prepare(stream);
+}
+
 uint32_t Camera3Device::getDeviceVersion() {
     ATRACE_CALL();
     Mutex::Autolock il(mInterfaceLock);
@@ -1409,6 +1440,11 @@
                 return NULL;
             }
         }
+        // Check if stream is being prepared
+        if (mInputStream->isPreparing()) {
+            CLOGE("Request references an input stream that's being prepared!");
+            return NULL;
+        }
 
         newRequest->mInputStream = mInputStream;
         newRequest->mSettings.erase(ANDROID_REQUEST_INPUT_STREAMS);
@@ -1441,6 +1477,11 @@
                 return NULL;
             }
         }
+        // Check if stream is being prepared
+        if (stream->isPreparing()) {
+            CLOGE("Request references an output stream that's being prepared!");
+            return NULL;
+        }
 
         newRequest->mOutputStreams.push(stream);
     }
@@ -1916,7 +1957,6 @@
     return true;
 }
 
-
 void Camera3Device::returnOutputBuffers(
         const camera3_stream_buffer_t *outputBuffers, size_t numBuffers,
         nsecs_t timestamp) {
@@ -2416,7 +2456,7 @@
 Camera3Device::RequestThread::RequestThread(wp<Camera3Device> parent,
         sp<StatusTracker> statusTracker,
         camera3_device_t *hal3Device) :
-        Thread(false),
+        Thread(/*canCallJava*/false),
         mParent(parent),
         mStatusTracker(statusTracker),
         mHal3Device(hal3Device),
@@ -2432,7 +2472,7 @@
     mStatusId = statusTracker->addComponent();
 }
 
-void Camera3Device::RequestThread::setNotifyCallback(
+void Camera3Device::RequestThread::setNotificationListener(
         NotificationListener *listener) {
     Mutex::Autolock l(mRequestLock);
     mListener = listener;
@@ -2846,6 +2886,26 @@
     return mLatestRequest;
 }
 
+bool Camera3Device::RequestThread::isStreamPending(
+        sp<Camera3StreamInterface>& stream) {
+    Mutex::Autolock l(mRequestLock);
+
+    for (const auto& request : mRequestQueue) {
+        for (const auto& s : request->mOutputStreams) {
+            if (stream == s) return true;
+        }
+        if (stream == request->mInputStream) return true;
+    }
+
+    for (const auto& request : mRepeatingRequests) {
+        for (const auto& s : request->mOutputStreams) {
+            if (stream == s) return true;
+        }
+        if (stream == request->mInputStream) return true;
+    }
+
+    return false;
+}
 
 void Camera3Device::RequestThread::cleanUpFailedRequest(
         camera3_capture_request_t &request,
@@ -3193,6 +3253,138 @@
     return OK;
 }
 
+/**
+ * PreparerThread inner class methods
+ */
+
+Camera3Device::PreparerThread::PreparerThread() :
+        Thread(/*canCallJava*/false), mActive(false), mCancelNow(false) {
+}
+
+Camera3Device::PreparerThread::~PreparerThread() {
+    Thread::requestExitAndWait();
+    if (mCurrentStream != nullptr) {
+        mCurrentStream->cancelPrepare();
+        ATRACE_ASYNC_END("stream prepare", mCurrentStream->getId());
+        mCurrentStream.clear();
+    }
+    clear();
+}
+
+status_t Camera3Device::PreparerThread::prepare(sp<Camera3StreamInterface>& stream) {
+    status_t res;
+
+    Mutex::Autolock l(mLock);
+
+    res = stream->startPrepare();
+    if (res == OK) {
+        // No preparation needed, fire listener right off
+        ALOGV("%s: Stream %d already prepared", __FUNCTION__, stream->getId());
+        if (mListener) {
+            mListener->notifyPrepared(stream->getId());
+        }
+        return OK;
+    } else if (res != NOT_ENOUGH_DATA) {
+        return res;
+    }
+
+    // Need to prepare, start up thread if necessary
+    if (!mActive) {
+        // mRunning will change to false before the thread fully shuts down, so wait to be sure it
+        // isn't running
+        Thread::requestExitAndWait();
+        res = Thread::run("C3PrepThread", PRIORITY_BACKGROUND);
+        if (res != OK) {
+            ALOGE("%s: Unable to start preparer stream: %d (%s)", __FUNCTION__, res, strerror(-res));
+            if (mListener) {
+                mListener->notifyPrepared(stream->getId());
+            }
+            return res;
+        }
+        mCancelNow = false;
+        mActive = true;
+        ALOGV("%s: Preparer stream started", __FUNCTION__);
+    }
+
+    // queue up the work
+    mPendingStreams.push_back(stream);
+    ALOGV("%s: Stream %d queued for preparing", __FUNCTION__, stream->getId());
+
+    return OK;
+}
+
+status_t Camera3Device::PreparerThread::clear() {
+    status_t res;
+
+    Mutex::Autolock l(mLock);
+
+    for (const auto& stream : mPendingStreams) {
+        stream->cancelPrepare();
+    }
+    mPendingStreams.clear();
+    mCancelNow = true;
+
+    return OK;
+}
+
+void Camera3Device::PreparerThread::setNotificationListener(NotificationListener *listener) {
+    Mutex::Autolock l(mLock);
+    mListener = listener;
+}
+
+bool Camera3Device::PreparerThread::threadLoop() {
+    status_t res;
+    {
+        Mutex::Autolock l(mLock);
+        if (mCurrentStream == nullptr) {
+            // End thread if done with work
+            if (mPendingStreams.empty()) {
+                ALOGV("%s: Preparer stream out of work", __FUNCTION__);
+                // threadLoop _must not_ re-acquire mLock after it sets mActive to false; would
+                // cause deadlock with prepare()'s requestExitAndWait triggered by !mActive.
+                mActive = false;
+                return false;
+            }
+
+            // Get next stream to prepare
+            auto it = mPendingStreams.begin();
+            mCurrentStream = *it;
+            mPendingStreams.erase(it);
+            ATRACE_ASYNC_BEGIN("stream prepare", mCurrentStream->getId());
+            ALOGV("%s: Preparing stream %d", __FUNCTION__, mCurrentStream->getId());
+        } else if (mCancelNow) {
+            mCurrentStream->cancelPrepare();
+            ATRACE_ASYNC_END("stream prepare", mCurrentStream->getId());
+            ALOGV("%s: Cancelling stream %d prepare", __FUNCTION__, mCurrentStream->getId());
+            mCurrentStream.clear();
+            mCancelNow = false;
+            return true;
+        }
+    }
+
+    res = mCurrentStream->prepareNextBuffer();
+    if (res == NOT_ENOUGH_DATA) return true;
+    if (res != OK) {
+        // Something bad happened; try to recover by cancelling prepare and
+        // signalling listener anyway
+        ALOGE("%s: Stream %d returned error %d (%s) during prepare", __FUNCTION__,
+                mCurrentStream->getId(), res, strerror(-res));
+        mCurrentStream->cancelPrepare();
+    }
+
+    // This stream has finished, notify listener
+    Mutex::Autolock l(mLock);
+    if (mListener) {
+        ALOGV("%s: Stream %d prepare done, signaling listener", __FUNCTION__,
+                mCurrentStream->getId());
+        mListener->notifyPrepared(mCurrentStream->getId());
+    }
+
+    ATRACE_ASYNC_END("stream prepare", mCurrentStream->getId());
+    mCurrentStream.clear();
+
+    return true;
+}
 
 /**
  * Static callback forwarding methods from HAL to instance
diff --git a/services/camera/libcameraservice/device3/Camera3Device.h b/services/camera/libcameraservice/device3/Camera3Device.h
index b08ba81..4fbcb2e 100644
--- a/services/camera/libcameraservice/device3/Camera3Device.h
+++ b/services/camera/libcameraservice/device3/Camera3Device.h
@@ -138,6 +138,8 @@
 
     virtual status_t flush(int64_t *lastFrameNumber = NULL);
 
+    virtual status_t prepare(int streamId);
+
     virtual uint32_t getDeviceVersion();
 
     virtual ssize_t getJpegBufferSize(uint32_t width, uint32_t height) const;
@@ -374,7 +376,7 @@
                 sp<camera3::StatusTracker> statusTracker,
                 camera3_device_t *hal3Device);
 
-        void     setNotifyCallback(NotificationListener *listener);
+        void     setNotificationListener(NotificationListener *listener);
 
         /**
          * Call after stream (re)-configuration is completed.
@@ -438,6 +440,12 @@
          */
         CameraMetadata getLatestRequest() const;
 
+        /**
+         * Returns true if the stream is a target of any queued or repeating
+         * capture request
+         */
+        bool isStreamPending(sp<camera3::Camera3StreamInterface>& stream);
+
       protected:
 
         virtual bool threadLoop();
@@ -559,7 +567,6 @@
         Vector<camera3_stream_buffer_t> pendingOutputBuffers;
 
 
-
         // Fields used by the partial result only
         struct PartialResultInFlight {
             // Set by process_capture_result once 3A has been sent to clients
@@ -610,7 +617,8 @@
                 resultExtras(extras),
                 hasInputBuffer(hasInput){
         }
-};
+    };
+
     // Map from frame number to the in-flight request state
     typedef KeyedVector<uint32_t, InFlightRequest> InFlightMap;
 
@@ -642,6 +650,45 @@
     sp<camera3::StatusTracker> mStatusTracker;
 
     /**
+     * Thread for preparing streams
+     */
+    class PreparerThread : private Thread, public virtual RefBase {
+      public:
+        PreparerThread();
+        ~PreparerThread();
+
+        void setNotificationListener(NotificationListener *listener);
+
+        /**
+         * Queue up a stream to be prepared. Streams are processed by
+         * a background thread in FIFO order
+         */
+        status_t prepare(sp<camera3::Camera3StreamInterface>& stream);
+
+        /**
+         * Cancel all current and pending stream preparation
+         */
+        status_t clear();
+
+      private:
+        Mutex mLock;
+
+        virtual bool threadLoop();
+
+        // Guarded by mLock
+
+        NotificationListener *mListener;
+        List<sp<camera3::Camera3StreamInterface> > mPendingStreams;
+        bool mActive;
+        bool mCancelNow;
+
+        // Only accessed by threadLoop and the destructor
+
+        sp<camera3::Camera3StreamInterface> mCurrentStream;
+    };
+    sp<PreparerThread> mPreparerThread;
+
+    /**
      * Output result queue and current HAL device 3A state
      */
 
diff --git a/services/camera/libcameraservice/device3/Camera3DummyStream.cpp b/services/camera/libcameraservice/device3/Camera3DummyStream.cpp
index 01edfff..ecb8ac8 100644
--- a/services/camera/libcameraservice/device3/Camera3DummyStream.cpp
+++ b/services/camera/libcameraservice/device3/Camera3DummyStream.cpp
@@ -87,7 +87,7 @@
     return OK;
 }
 
-status_t Camera3DummyStream::getEndpointUsage(uint32_t *usage) {
+status_t Camera3DummyStream::getEndpointUsage(uint32_t *usage) const {
     *usage = DUMMY_USAGE;
     return OK;
 }
diff --git a/services/camera/libcameraservice/device3/Camera3DummyStream.h b/services/camera/libcameraservice/device3/Camera3DummyStream.h
index d023c57..3a3dbf4 100644
--- a/services/camera/libcameraservice/device3/Camera3DummyStream.h
+++ b/services/camera/libcameraservice/device3/Camera3DummyStream.h
@@ -89,7 +89,7 @@
 
     virtual status_t configureQueueLocked();
 
-    virtual status_t getEndpointUsage(uint32_t *usage);
+    virtual status_t getEndpointUsage(uint32_t *usage) const;
 
 }; // class Camera3DummyStream
 
diff --git a/services/camera/libcameraservice/device3/Camera3IOStreamBase.cpp b/services/camera/libcameraservice/device3/Camera3IOStreamBase.cpp
index 8696413..23b1c45 100644
--- a/services/camera/libcameraservice/device3/Camera3IOStreamBase.cpp
+++ b/services/camera/libcameraservice/device3/Camera3IOStreamBase.cpp
@@ -67,13 +67,18 @@
 void Camera3IOStreamBase::dump(int fd, const Vector<String16> &args) const {
     (void) args;
     String8 lines;
+
+    uint32_t consumerUsage = 0;
+    status_t res = getEndpointUsage(&consumerUsage);
+    if (res != OK) consumerUsage = 0;
+
     lines.appendFormat("      State: %d\n", mState);
-    lines.appendFormat("      Dims: %d x %d, format 0x%x\n",
+    lines.appendFormat("      Dims: %d x %d, format 0x%x, dataspace 0x%x\n",
             camera3_stream::width, camera3_stream::height,
-            camera3_stream::format);
+            camera3_stream::format, camera3_stream::data_space);
     lines.appendFormat("      Max size: %zu\n", mMaxSize);
-    lines.appendFormat("      Usage: %d, max HAL buffers: %d\n",
-            camera3_stream::usage, camera3_stream::max_buffers);
+    lines.appendFormat("      Combined usage: %d, max HAL buffers: %d\n",
+            camera3_stream::usage | consumerUsage, camera3_stream::max_buffers);
     lines.appendFormat("      Frames produced: %d, last timestamp: %" PRId64 " ns\n",
             mFrameCount, mLastTimestamp);
     lines.appendFormat("      Total buffers: %zu, currently dequeued: %zu\n",
@@ -156,13 +161,11 @@
 
     // Inform tracker about becoming busy
     if (mHandoutTotalBufferCount == 0 && mState != STATE_IN_CONFIG &&
-            mState != STATE_IN_RECONFIG) {
+            mState != STATE_IN_RECONFIG && mState != STATE_PREPARING) {
         /**
          * Avoid a spurious IDLE->ACTIVE->IDLE transition when using buffers
          * before/after register_stream_buffers during initial configuration
-         * or re-configuration.
-         *
-         * TODO: IN_CONFIG and IN_RECONFIG checks only make sense for <HAL3.2
+         * or re-configuration, or during prepare pre-allocation
          */
         sp<StatusTracker> statusTracker = mStatusTracker.promote();
         if (statusTracker != 0) {
@@ -177,9 +180,11 @@
 }
 
 status_t Camera3IOStreamBase::getBufferPreconditionCheckLocked() const {
-    // Allow dequeue during IN_[RE]CONFIG for registration
+    // Allow dequeue during IN_[RE]CONFIG for registration, in
+    // PREPARING for pre-allocation
     if (mState != STATE_CONFIGURED &&
-            mState != STATE_IN_CONFIG && mState != STATE_IN_RECONFIG) {
+            mState != STATE_IN_CONFIG && mState != STATE_IN_RECONFIG &&
+            mState != STATE_PREPARING) {
         ALOGE("%s: Stream %d: Can't get buffers in unconfigured state %d",
                 __FUNCTION__, mId, mState);
         return INVALID_OPERATION;
@@ -240,13 +245,11 @@
 
     mHandoutTotalBufferCount--;
     if (mHandoutTotalBufferCount == 0 && mState != STATE_IN_CONFIG &&
-            mState != STATE_IN_RECONFIG) {
+            mState != STATE_IN_RECONFIG && mState != STATE_PREPARING) {
         /**
          * Avoid a spurious IDLE->ACTIVE->IDLE transition when using buffers
          * before/after register_stream_buffers during initial configuration
-         * or re-configuration.
-         *
-         * TODO: IN_CONFIG and IN_RECONFIG checks only make sense for <HAL3.2
+         * or re-configuration, or during prepare pre-allocation
          */
         ALOGV("%s: Stream %d: All buffers returned; now idle", __FUNCTION__,
                 mId);
diff --git a/services/camera/libcameraservice/device3/Camera3IOStreamBase.h b/services/camera/libcameraservice/device3/Camera3IOStreamBase.h
index abcf2b1..f5727e8 100644
--- a/services/camera/libcameraservice/device3/Camera3IOStreamBase.h
+++ b/services/camera/libcameraservice/device3/Camera3IOStreamBase.h
@@ -84,7 +84,7 @@
 
     virtual size_t   getHandoutInputBufferCountLocked();
 
-    virtual status_t getEndpointUsage(uint32_t *usage) = 0;
+    virtual status_t getEndpointUsage(uint32_t *usage) const = 0;
 
     status_t getBufferPreconditionCheckLocked() const;
     status_t returnBufferPreconditionCheckLocked() const;
diff --git a/services/camera/libcameraservice/device3/Camera3InputStream.cpp b/services/camera/libcameraservice/device3/Camera3InputStream.cpp
index fa97e57..84c5754 100644
--- a/services/camera/libcameraservice/device3/Camera3InputStream.cpp
+++ b/services/camera/libcameraservice/device3/Camera3InputStream.cpp
@@ -275,7 +275,7 @@
     return OK;
 }
 
-status_t Camera3InputStream::getEndpointUsage(uint32_t *usage) {
+status_t Camera3InputStream::getEndpointUsage(uint32_t *usage) const {
     // Per HAL3 spec, input streams have 0 for their initial usage field.
     *usage = 0;
     return OK;
diff --git a/services/camera/libcameraservice/device3/Camera3InputStream.h b/services/camera/libcameraservice/device3/Camera3InputStream.h
index 7ba36c9..9f3de10 100644
--- a/services/camera/libcameraservice/device3/Camera3InputStream.h
+++ b/services/camera/libcameraservice/device3/Camera3InputStream.h
@@ -75,7 +75,7 @@
 
     virtual status_t configureQueueLocked();
 
-    virtual status_t getEndpointUsage(uint32_t *usage);
+    virtual status_t getEndpointUsage(uint32_t *usage) const;
 
 }; // class Camera3InputStream
 
diff --git a/services/camera/libcameraservice/device3/Camera3OutputStream.cpp b/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
index 8d9b360..7a0331b 100644
--- a/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
+++ b/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
@@ -209,6 +209,13 @@
         }
     }
     mLock.lock();
+
+    // Once a valid buffer has been returned to the queue, can no longer
+    // dequeue all buffers for preallocation.
+    if (buffer.status != CAMERA3_BUFFER_STATUS_ERROR) {
+        mStreamUnpreparable = true;
+    }
+
     if (res != OK) {
         close(anwReleaseFence);
     }
@@ -390,7 +397,7 @@
     return OK;
 }
 
-status_t Camera3OutputStream::getEndpointUsage(uint32_t *usage) {
+status_t Camera3OutputStream::getEndpointUsage(uint32_t *usage) const {
 
     status_t res;
     int32_t u = 0;
diff --git a/services/camera/libcameraservice/device3/Camera3OutputStream.h b/services/camera/libcameraservice/device3/Camera3OutputStream.h
index 12b2ebb..513b695 100644
--- a/services/camera/libcameraservice/device3/Camera3OutputStream.h
+++ b/services/camera/libcameraservice/device3/Camera3OutputStream.h
@@ -99,7 +99,7 @@
 
     virtual status_t configureQueueLocked();
 
-    virtual status_t getEndpointUsage(uint32_t *usage);
+    virtual status_t getEndpointUsage(uint32_t *usage) const;
 
 }; // class Camera3OutputStream
 
diff --git a/services/camera/libcameraservice/device3/Camera3Stream.cpp b/services/camera/libcameraservice/device3/Camera3Stream.cpp
index d3c5cc3..3821da1 100644
--- a/services/camera/libcameraservice/device3/Camera3Stream.cpp
+++ b/services/camera/libcameraservice/device3/Camera3Stream.cpp
@@ -194,6 +194,11 @@
         return OK;
     }
 
+    // Reset prepared state, since buffer config has changed, and existing
+    // allocations are no longer valid
+    mPrepared = false;
+    mStreamUnpreparable = false;
+
     status_t res;
     res = configureQueueLocked();
     if (res != OK) {
@@ -244,6 +249,125 @@
     return OK;
 }
 
+bool Camera3Stream::isUnpreparable() {
+    ATRACE_CALL();
+
+    Mutex::Autolock l(mLock);
+    return mStreamUnpreparable;
+}
+
+status_t Camera3Stream::startPrepare() {
+    ATRACE_CALL();
+
+    Mutex::Autolock l(mLock);
+    status_t res = OK;
+
+    // This function should be only called when the stream is configured already.
+    if (mState != STATE_CONFIGURED) {
+        ALOGE("%s: Stream %d: Can't prepare stream if stream is not in CONFIGURED "
+                "state %d", __FUNCTION__, mId, mState);
+        return INVALID_OPERATION;
+    }
+
+    // This function can't be called if the stream has already received filled
+    // buffers
+    if (mStreamUnpreparable) {
+        ALOGE("%s: Stream %d: Can't prepare stream that's already in use",
+                __FUNCTION__, mId);
+        return INVALID_OPERATION;
+    }
+
+    if (getHandoutOutputBufferCountLocked() > 0) {
+        ALOGE("%s: Stream %d: Can't prepare stream that has outstanding buffers",
+                __FUNCTION__, mId);
+        return INVALID_OPERATION;
+    }
+
+    if (mPrepared) return OK;
+
+    size_t bufferCount = getBufferCountLocked();
+
+    mPreparedBuffers.insertAt(camera3_stream_buffer_t(), /*index*/0, bufferCount);
+    mPreparedBufferIdx = 0;
+
+    mState = STATE_PREPARING;
+
+    return NOT_ENOUGH_DATA;
+}
+
+bool Camera3Stream::isPreparing() const {
+    Mutex::Autolock l(mLock);
+    return mState == STATE_PREPARING;
+}
+
+status_t Camera3Stream::prepareNextBuffer() {
+    ATRACE_CALL();
+
+    Mutex::Autolock l(mLock);
+    status_t res = OK;
+
+    // This function should be only called when the stream is preparing
+    if (mState != STATE_PREPARING) {
+        ALOGE("%s: Stream %d: Can't prepare buffer if stream is not in PREPARING "
+                "state %d", __FUNCTION__, mId, mState);
+        return INVALID_OPERATION;
+    }
+
+    // Get next buffer - this may allocate, and take a while for large buffers
+    res = getBufferLocked( &mPreparedBuffers.editItemAt(mPreparedBufferIdx) );
+    if (res != OK) {
+        ALOGE("%s: Stream %d: Unable to allocate buffer %d during preparation",
+                __FUNCTION__, mId, mPreparedBufferIdx);
+        return NO_INIT;
+    }
+
+    mPreparedBufferIdx++;
+
+    // Check if we still have buffers left to allocate
+    if (mPreparedBufferIdx < mPreparedBuffers.size()) {
+        return NOT_ENOUGH_DATA;
+    }
+
+    // Done with prepare - mark stream as such, and return all buffers
+    // via cancelPrepare
+    mPrepared = true;
+
+    return cancelPrepareLocked();
+}
+
+status_t Camera3Stream::cancelPrepare() {
+    ATRACE_CALL();
+
+    Mutex::Autolock l(mLock);
+
+    return cancelPrepareLocked();
+}
+
+status_t Camera3Stream::cancelPrepareLocked() {
+    status_t res = OK;
+
+    // This function should be only called when the stream is mid-preparing.
+    if (mState != STATE_PREPARING) {
+        ALOGE("%s: Stream %d: Can't cancel prepare stream if stream is not in "
+                "PREPARING state %d", __FUNCTION__, mId, mState);
+        return INVALID_OPERATION;
+    }
+
+    // Return all valid buffers to stream, in ERROR state to indicate
+    // they weren't filled.
+    for (size_t i = 0; i < mPreparedBufferIdx; i++) {
+        mPreparedBuffers.editItemAt(i).release_fence = -1;
+        mPreparedBuffers.editItemAt(i).status = CAMERA3_BUFFER_STATUS_ERROR;
+        returnBufferLocked(mPreparedBuffers[i], 0);
+    }
+    mPreparedBuffers.clear();
+    mPreparedBufferIdx = 0;
+
+    mState = STATE_CONFIGURED;
+
+    return res;
+}
+
 status_t Camera3Stream::getBuffer(camera3_stream_buffer *buffer) {
     ATRACE_CALL();
     Mutex::Autolock l(mLock);
@@ -427,15 +551,13 @@
             ALOGE("%s: register_stream_buffers is deprecated in HAL3.2; "
                     "must be set to NULL in camera3_device::ops", __FUNCTION__);
             return INVALID_OPERATION;
-        } else {
-            ALOGD("%s: Skipping NULL check for deprecated register_stream_buffers", __FUNCTION__);
         }
 
         return OK;
-    } else {
-        ALOGV("%s: register_stream_buffers using deprecated code path", __FUNCTION__);
     }
 
+    ALOGV("%s: register_stream_buffers using deprecated code path", __FUNCTION__);
+
     status_t res;
 
     size_t bufferCount = getBufferCountLocked();
@@ -491,6 +613,8 @@
         returnBufferLocked(streamBuffers[i], 0);
     }
 
+    mPrepared = true;
+
     return res;
 }
 
diff --git a/services/camera/libcameraservice/device3/Camera3Stream.h b/services/camera/libcameraservice/device3/Camera3Stream.h
index e89361e..0543c66 100644
--- a/services/camera/libcameraservice/device3/Camera3Stream.h
+++ b/services/camera/libcameraservice/device3/Camera3Stream.h
@@ -57,8 +57,15 @@
  *    re-registering buffers with HAL.
  *
  *  STATE_CONFIGURED: Stream is configured, and has registered buffers with the
- *    HAL. The stream's getBuffer/returnBuffer work. The priv pointer may still be
- *    modified.
+ *    HAL (if necessary). The stream's getBuffer/returnBuffer work. The priv
+ *    pointer may still be modified.
+ *
+ *  STATE_PREPARING: The stream's buffers are being pre-allocated for use.  On
+ *    older HALs, this is done as part of configuration, but in newer HALs
+ *    buffers may be allocated at time of first use. But some use cases require
+ *    buffer allocation upfront, to minmize disruption due to lengthy allocation
+ *    duration.  In this state, only prepareNextBuffer() and cancelPrepare()
+ *    may be called.
  *
  * Transition table:
  *
@@ -82,6 +89,12 @@
  *    STATE_CONFIGURED     => STATE_CONSTRUCTED:
  *        When disconnect() is called after making sure stream is idle with
  *        waitUntilIdle().
+ *    STATE_CONFIGURED     => STATE_PREPARING:
+ *        When startPrepare is called before the stream has a buffer
+ *        queued back into it for the first time.
+ *    STATE_PREPARING      => STATE_CONFIGURED:
+ *        When sufficient prepareNextBuffer calls have been made to allocate
+ *        all stream buffers, or cancelPrepare is called.
  *
  * Status Tracking:
  *    Each stream is tracked by StatusTracker as a separate component,
@@ -167,6 +180,73 @@
     status_t         cancelConfiguration();
 
     /**
+     * Determine whether the stream has already become in-use (has received
+     * a valid filled buffer), which determines if a stream can still have
+     * prepareNextBuffer called on it.
+     */
+    bool             isUnpreparable();
+
+    /**
+     * Start stream preparation. May only be called in the CONFIGURED state,
+     * when no valid buffers have yet been returned to this stream.
+     *
+     * If no prepartion is necessary, returns OK and does not transition to
+     * PREPARING state. Otherwise, returns NOT_ENOUGH_DATA and transitions
+     * to PREPARING.
+     *
+     * This call performs no allocation, so is quick to call.
+     *
+     * Returns:
+     *    OK if no more buffers need to be preallocated
+     *    NOT_ENOUGH_DATA if calls to prepareNextBuffer are needed to finish
+     *        buffer pre-allocation, and transitions to the PREPARING state.
+     *    NO_INIT in case of a serious error from the HAL device
+     *    INVALID_OPERATION if called when not in CONFIGURED state, or a
+     *        valid buffer has already been returned to this stream.
+     */
+    status_t         startPrepare();
+
+    /**
+     * Check if the stream is mid-preparing.
+     */
+    bool             isPreparing() const;
+
+    /**
+     * Continue stream buffer preparation by allocating the next
+     * buffer for this stream.  May only be called in the PREPARED state.
+     *
+     * Returns OK and transitions to the CONFIGURED state if all buffers
+     * are allocated after the call concludes. Otherwise returns NOT_ENOUGH_DATA.
+     *
+     * This call allocates one buffer, which may take several milliseconds for
+     * large buffers.
+     *
+     * Returns:
+     *    OK if no more buffers need to be preallocated, and transitions
+     *        to the CONFIGURED state.
+     *    NOT_ENOUGH_DATA if more calls to prepareNextBuffer are needed to finish
+     *        buffer pre-allocation.
+     *    NO_INIT in case of a serious error from the HAL device
+     *    INVALID_OPERATION if called when not in CONFIGURED state, or a
+     *        valid buffer has already been returned to this stream.
+     */
+    status_t         prepareNextBuffer();
+
+    /**
+     * Cancel stream preparation early. In case allocation needs to be
+     * stopped, this method transitions the stream back to the CONFIGURED state.
+     * Buffers that have been allocated with prepareNextBuffer remain that way,
+     * but a later use of prepareNextBuffer will require just as many
+     * calls as if the earlier prepare attempt had not existed.
+     *
+     * Returns:
+     *    OK if cancellation succeeded, and transitions to the CONFIGURED state
+     *    INVALID_OPERATION if not in the PREPARING state
+     *    NO_INIT in case of a serious error from the HAL device
+     */
+    status_t        cancelPrepare();
+
+    /**
      * Fill in the camera3_stream_buffer with the next valid buffer for this
      * stream, to hand over to the HAL.
      *
@@ -263,7 +343,8 @@
         STATE_CONSTRUCTED,
         STATE_IN_CONFIG,
         STATE_IN_RECONFIG,
-        STATE_CONFIGURED
+        STATE_CONFIGURED,
+        STATE_PREPARING
     } mState;
 
     mutable Mutex mLock;
@@ -312,13 +393,17 @@
 
     // Get the usage flags for the other endpoint, or return
     // INVALID_OPERATION if they cannot be obtained.
-    virtual status_t getEndpointUsage(uint32_t *usage) = 0;
+    virtual status_t getEndpointUsage(uint32_t *usage) const = 0;
 
     // Tracking for idle state
     wp<StatusTracker> mStatusTracker;
     // Status tracker component ID
     int mStatusId;
 
+    // Tracking for stream prepare - whether this stream can still have
+    // prepareNextBuffer called on it.
+    bool mStreamUnpreparable;
+
   private:
     uint32_t oldUsage;
     uint32_t oldMaxBuffers;
@@ -333,6 +418,18 @@
                                   bool acquired, bool output);
     List<wp<Camera3StreamBufferListener> > mBufferListenerList;
 
+    status_t        cancelPrepareLocked();
+
+    // Tracking for PREPARING state
+
+    // State of buffer preallocation. Only true if either prepareNextBuffer
+    // has been called sufficient number of times, or stream configuration
+    // had to register buffers with the HAL
+    bool mPrepared;
+
+    Vector<camera3_stream_buffer_t> mPreparedBuffers;
+    size_t mPreparedBufferIdx;
+
 }; // class Camera3Stream
 
 }; // namespace camera3
diff --git a/services/camera/libcameraservice/device3/Camera3StreamInterface.h b/services/camera/libcameraservice/device3/Camera3StreamInterface.h
index ea90dd9..d177b57 100644
--- a/services/camera/libcameraservice/device3/Camera3StreamInterface.h
+++ b/services/camera/libcameraservice/device3/Camera3StreamInterface.h
@@ -89,6 +89,68 @@
     virtual status_t cancelConfiguration() = 0;
 
     /**
+     * Determine whether the stream has already become in-use (has received
+     * a valid filled buffer), which determines if a stream can still have
+     * prepareNextBuffer called on it.
+     */
+    virtual bool     isUnpreparable() = 0;
+
+    /**
+     * Start stream preparation. May only be called in the CONFIGURED state,
+     * when no valid buffers have yet been returned to this stream.
+     *
+     * If no prepartion is necessary, returns OK and does not transition to
+     * PREPARING state. Otherwise, returns NOT_ENOUGH_DATA and transitions
+     * to PREPARING.
+     *
+     * Returns:
+     *    OK if no more buffers need to be preallocated
+     *    NOT_ENOUGH_DATA if calls to prepareNextBuffer are needed to finish
+     *        buffer pre-allocation, and transitions to the PREPARING state.
+     *    NO_INIT in case of a serious error from the HAL device
+     *    INVALID_OPERATION if called when not in CONFIGURED state, or a
+     *        valid buffer has already been returned to this stream.
+     */
+    virtual status_t startPrepare() = 0;
+
+    /**
+     * Check if the stream is mid-preparing.
+     */
+    virtual bool     isPreparing() const = 0;
+
+    /**
+     * Continue stream buffer preparation by allocating the next
+     * buffer for this stream.  May only be called in the PREPARED state.
+     *
+     * Returns OK and transitions to the CONFIGURED state if all buffers
+     * are allocated after the call concludes. Otherwise returns NOT_ENOUGH_DATA.
+     *
+     * Returns:
+     *    OK if no more buffers need to be preallocated, and transitions
+     *        to the CONFIGURED state.
+     *    NOT_ENOUGH_DATA if more calls to prepareNextBuffer are needed to finish
+     *        buffer pre-allocation.
+     *    NO_INIT in case of a serious error from the HAL device
+     *    INVALID_OPERATION if called when not in CONFIGURED state, or a
+     *        valid buffer has already been returned to this stream.
+     */
+    virtual status_t prepareNextBuffer() = 0;
+
+    /**
+     * Cancel stream preparation early. In case allocation needs to be
+     * stopped, this method transitions the stream back to the CONFIGURED state.
+     * Buffers that have been allocated with prepareNextBuffer remain that way,
+     * but a later use of prepareNextBuffer will require just as many
+     * calls as if the earlier prepare attempt had not existed.
+     *
+     * Returns:
+     *    OK if cancellation succeeded, and transitions to the CONFIGURED state
+     *    INVALID_OPERATION if not in the PREPARING state
+     *    NO_INIT in case of a serious error from the HAL device
+     */
+    virtual status_t cancelPrepare() = 0;
+
+    /**
      * Fill in the camera3_stream_buffer with the next valid buffer for this
      * stream, to hand over to the HAL.
      *