diff --git a/services/surfaceflinger/Android.bp b/services/surfaceflinger/Android.bp
index d500ae8..e176569 100644
--- a/services/surfaceflinger/Android.bp
+++ b/services/surfaceflinger/Android.bp
@@ -148,6 +148,46 @@
     },
 }
 
+// libsurfaceflinger_backend_{headers|sources} are a step towards pulling out
+// the "backend" sources to clean up the dependency graph between
+// CompositionEngine and SurfaceFlinger. Completing the cleanup would require
+// moving the headers in particular so that the dependency can strictly be a
+// DAG. There would certainly be additional cleanups: VirtualDisplaySurface.cpp
+// and FrameBufferSurface.cpp likely belong in CompositionEngine for example.
+cc_library_headers {
+    name: "libsurfaceflinger_backend_headers",
+    export_include_dirs: ["."],
+    static_libs: ["libserviceutils"],
+    export_static_lib_headers: ["libserviceutils"],
+
+    shared_libs: [
+        "android.hardware.configstore-utils",
+        "android.hardware.configstore@1.0",
+        "android.hardware.configstore@1.1",
+        "libbinder_ndk",
+    ],
+    export_shared_lib_headers: [
+        "android.hardware.configstore-utils",
+        "android.hardware.configstore@1.0",
+        "android.hardware.configstore@1.1",
+        "libbinder_ndk",
+    ],
+}
+
+filegroup {
+    name: "libsurfaceflinger_backend_sources",
+    srcs: [
+        "DisplayHardware/AidlComposerHal.cpp",
+        "DisplayHardware/ComposerHal.cpp",
+        "DisplayHardware/FramebufferSurface.cpp",
+        "DisplayHardware/HWC2.cpp",
+        "DisplayHardware/HWComposer.cpp",
+        "DisplayHardware/HidlComposerHal.cpp",
+        "DisplayHardware/PowerAdvisor.cpp",
+        "DisplayHardware/VirtualDisplaySurface.cpp",
+    ],
+}
+
 cc_library_headers {
     name: "libsurfaceflinger_headers",
     export_include_dirs: ["."],
@@ -158,20 +198,13 @@
 filegroup {
     name: "libsurfaceflinger_sources",
     srcs: [
+        ":libsurfaceflinger_backend_sources",
         "BackgroundExecutor.cpp",
         "Client.cpp",
         "ClientCache.cpp",
         "Display/DisplayModeController.cpp",
         "Display/DisplaySnapshot.cpp",
         "DisplayDevice.cpp",
-        "DisplayHardware/AidlComposerHal.cpp",
-        "DisplayHardware/ComposerHal.cpp",
-        "DisplayHardware/FramebufferSurface.cpp",
-        "DisplayHardware/HWC2.cpp",
-        "DisplayHardware/HWComposer.cpp",
-        "DisplayHardware/HidlComposerHal.cpp",
-        "DisplayHardware/PowerAdvisor.cpp",
-        "DisplayHardware/VirtualDisplaySurface.cpp",
         "DisplayRenderArea.cpp",
         "Effects/Daltonizer.cpp",
         "FrontEnd/LayerCreationArgs.cpp",
diff --git a/services/surfaceflinger/CompositionEngine/Android.bp b/services/surfaceflinger/CompositionEngine/Android.bp
index b4ac9ba..7095b9d 100644
--- a/services/surfaceflinger/CompositionEngine/Android.bp
+++ b/services/surfaceflinger/CompositionEngine/Android.bp
@@ -59,7 +59,7 @@
         "android.hardware.graphics.composer@2.3-command-buffer",
         "android.hardware.graphics.composer@2.4-command-buffer",
         "android.hardware.graphics.composer3-command-buffer",
-        "libsurfaceflinger_headers",
+        "libsurfaceflinger_backend_headers",
     ],
 }
 
@@ -141,6 +141,8 @@
     ],
     srcs: [
         ":libcompositionengine_sources",
+        ":libsurfaceflinger_backend_mock_sources",
+        ":libsurfaceflinger_backend_sources",
         "tests/planner/CachedSetTest.cpp",
         "tests/planner/FlattenerTest.cpp",
         "tests/planner/LayerStateTest.cpp",
@@ -151,14 +153,14 @@
         "tests/DisplayTest.cpp",
         "tests/HwcAsyncWorkerTest.cpp",
         "tests/HwcBufferCacheTest.cpp",
-        "tests/MockHWC2.cpp",
-        "tests/MockHWComposer.cpp",
-        "tests/MockPowerAdvisor.cpp",
         "tests/OutputLayerTest.cpp",
         "tests/OutputTest.cpp",
         "tests/ProjectionSpaceTest.cpp",
         "tests/RenderSurfaceTest.cpp",
     ],
+    header_libs: [
+        "libsurfaceflinger_backend_mock_headers",
+    ],
     static_libs: [
         "libcompositionengine_mocks",
         "libgui_mocks",
@@ -167,6 +169,7 @@
         "libgtest",
     ],
     shared_libs: [
+        "libbinder_ndk",
         // For some reason, libvulkan isn't picked up from librenderengine
         // Probably ASAN related?
         "libvulkan",
diff --git a/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp b/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp
index 48ebc32..3e0c390 100644
--- a/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/CompositionEngineTest.cpp
@@ -26,9 +26,8 @@
 #include <gtest/gtest.h>
 #include <renderengine/mock/RenderEngine.h>
 
-#include "MockHWComposer.h"
 #include "TimeStats/TimeStats.h"
-#include "gmock/gmock.h"
+#include "mock/DisplayHardware/MockHWComposer.h"
 
 using namespace com::android::graphics::surfaceflinger;
 
diff --git a/services/surfaceflinger/CompositionEngine/tests/DisplayTest.cpp b/services/surfaceflinger/CompositionEngine/tests/DisplayTest.cpp
index 9c0e62c..416001e 100644
--- a/services/surfaceflinger/CompositionEngine/tests/DisplayTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/DisplayTest.cpp
@@ -36,10 +36,10 @@
 #include <ui/Rect.h>
 #include <ui/StaticDisplayInfo.h>
 
-#include "MockHWC2.h"
-#include "MockHWComposer.h"
-#include "MockPowerAdvisor.h"
 #include "ftl/future.h"
+#include "mock/DisplayHardware/MockHWC2.h"
+#include "mock/DisplayHardware/MockHWComposer.h"
+#include "mock/DisplayHardware/MockPowerAdvisor.h"
 
 #include <aidl/android/hardware/graphics/composer3/Composition.h>
 
diff --git a/services/surfaceflinger/CompositionEngine/tests/MockHWC2.cpp b/services/surfaceflinger/CompositionEngine/tests/MockHWC2.cpp
deleted file mode 100644
index 0baa79d..0000000
--- a/services/surfaceflinger/CompositionEngine/tests/MockHWC2.cpp
+++ /dev/null
@@ -1,32 +0,0 @@
-/*
- * Copyright 2019 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.
- */
-
-#include "MockHWC2.h"
-
-namespace android::HWC2 {
-
-// This will go away once HWC2::Layer is moved into the "backend" library
-Layer::~Layer() = default;
-
-namespace mock {
-
-// The Google Mock documentation recommends explicit non-header instantiations
-// for better compile time performance.
-Layer::Layer() = default;
-Layer::~Layer() = default;
-
-} // namespace mock
-} // namespace android::HWC2
diff --git a/services/surfaceflinger/CompositionEngine/tests/MockHWC2.h b/services/surfaceflinger/CompositionEngine/tests/MockHWC2.h
deleted file mode 100644
index 26b5f4a..0000000
--- a/services/surfaceflinger/CompositionEngine/tests/MockHWC2.h
+++ /dev/null
@@ -1,86 +0,0 @@
-/*
- * Copyright 2019 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.
- */
-
-#pragma once
-
-#include <gmock/gmock.h>
-#include <ui/Fence.h>
-#include <ui/FloatRect.h>
-#include <ui/GraphicBuffer.h>
-#include <ui/Rect.h>
-#include <ui/Region.h>
-#include <ui/Transform.h>
-
-// TODO(b/129481165): remove the #pragma below and fix conversion issues
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wconversion"
-#pragma clang diagnostic ignored "-Wextra"
-
-#include <ui/GraphicTypes.h>
-#include "DisplayHardware/HWC2.h"
-
-#include <aidl/android/hardware/graphics/composer3/Composition.h>
-#include <aidl/android/hardware/graphics/composer3/Luts.h>
-
-// TODO(b/129481165): remove the #pragma below and fix conversion issues
-#pragma clang diagnostic pop // ignored "-Wconversion -Wextra"
-
-namespace android {
-namespace HWC2 {
-namespace mock {
-
-namespace hal = android::hardware::graphics::composer::hal;
-
-using Error = hal::Error;
-
-class Layer : public HWC2::Layer {
-public:
-    Layer();
-    ~Layer() override;
-
-    MOCK_CONST_METHOD0(getId, hal::HWLayerId());
-
-    MOCK_METHOD2(setCursorPosition, Error(int32_t, int32_t));
-    MOCK_METHOD3(setBuffer,
-                 Error(uint32_t, const android::sp<android::GraphicBuffer>&,
-                       const android::sp<android::Fence>&));
-    MOCK_METHOD2(setBufferSlotsToClear, Error(const std::vector<uint32_t>&, uint32_t));
-    MOCK_METHOD1(setSurfaceDamage, Error(const android::Region&));
-    MOCK_METHOD1(setBlendMode, Error(hal::BlendMode));
-    MOCK_METHOD1(setColor, Error(aidl::android::hardware::graphics::composer3::Color));
-    MOCK_METHOD1(setCompositionType,
-                 Error(aidl::android::hardware::graphics::composer3::Composition));
-    MOCK_METHOD1(setDataspace, Error(android::ui::Dataspace));
-    MOCK_METHOD2(setPerFrameMetadata, Error(const int32_t, const android::HdrMetadata&));
-    MOCK_METHOD1(setDisplayFrame, Error(const android::Rect&));
-    MOCK_METHOD1(setPlaneAlpha, Error(float));
-    MOCK_METHOD1(setSidebandStream, Error(const native_handle_t*));
-    MOCK_METHOD1(setSourceCrop, Error(const android::FloatRect&));
-    MOCK_METHOD1(setTransform, Error(hal::Transform));
-    MOCK_METHOD1(setVisibleRegion, Error(const android::Region&));
-    MOCK_METHOD1(setZOrder, Error(uint32_t));
-
-    MOCK_METHOD1(setColorTransform, Error(const android::mat4&));
-    MOCK_METHOD3(setLayerGenericMetadata,
-                 Error(const std::string&, bool, const std::vector<uint8_t>&));
-    MOCK_METHOD1(setBrightness, Error(float));
-    MOCK_METHOD1(setBlockingRegion, Error(const android::Region&));
-    MOCK_METHOD(Error, setLuts, (aidl::android::hardware::graphics::composer3::Luts&));
-};
-
-} // namespace mock
-} // namespace HWC2
-} // namespace android
diff --git a/services/surfaceflinger/CompositionEngine/tests/MockHWComposer.h b/services/surfaceflinger/CompositionEngine/tests/MockHWComposer.h
deleted file mode 100644
index 5c55ce7..0000000
--- a/services/surfaceflinger/CompositionEngine/tests/MockHWComposer.h
+++ /dev/null
@@ -1,159 +0,0 @@
-/*
- * Copyright 2018 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.
- */
-
-#pragma once
-
-#include <compositionengine/Output.h>
-#include <gmock/gmock.h>
-
-// TODO(b/129481165): remove the #pragma below and fix conversion issues
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wconversion"
-#pragma clang diagnostic ignored "-Wextra"
-
-#include "DisplayHardware/HWComposer.h"
-
-// TODO(b/129481165): remove the #pragma below and fix conversion issues
-#pragma clang diagnostic pop // ignored "-Wconversion -Wextra"
-
-namespace android {
-namespace mock {
-
-namespace hal = android::hardware::graphics::composer::hal;
-
-class HWComposer : public android::HWComposer {
-public:
-    HWComposer();
-    ~HWComposer() override;
-
-    MOCK_METHOD1(setCallback, void(HWC2::ComposerCallback&));
-    MOCK_CONST_METHOD3(getDisplayIdentificationData,
-                       bool(hal::HWDisplayId, uint8_t*, DisplayIdentificationData*));
-    MOCK_CONST_METHOD1(hasCapability,
-                       bool(aidl::android::hardware::graphics::composer3::Capability));
-    MOCK_CONST_METHOD2(hasDisplayCapability,
-                       bool(HalDisplayId,
-                            aidl::android::hardware::graphics::composer3::DisplayCapability));
-
-    MOCK_CONST_METHOD0(getMaxVirtualDisplayCount, size_t());
-    MOCK_CONST_METHOD0(getMaxVirtualDisplayDimension, size_t());
-    MOCK_METHOD3(allocateVirtualDisplay, bool(HalVirtualDisplayId, ui::Size, ui::PixelFormat*));
-    MOCK_METHOD3(allocatePhysicalDisplay,
-                 void(hal::HWDisplayId, PhysicalDisplayId, std::optional<ui::Size>));
-
-    MOCK_METHOD1(createLayer, std::shared_ptr<HWC2::Layer>(HalDisplayId));
-    MOCK_METHOD(status_t, getDeviceCompositionChanges,
-                (HalDisplayId, bool, std::optional<std::chrono::steady_clock::time_point>, nsecs_t,
-                 Fps, std::optional<android::HWComposer::DeviceRequestedChanges>*));
-    MOCK_METHOD(status_t, setClientTarget,
-                (HalDisplayId, uint32_t, const sp<Fence>&, const sp<GraphicBuffer>&, ui::Dataspace,
-                 float),
-                (override));
-    MOCK_METHOD2(presentAndGetReleaseFences,
-                 status_t(HalDisplayId, std::optional<std::chrono::steady_clock::time_point>));
-    MOCK_METHOD(status_t, executeCommands, (HalDisplayId));
-    MOCK_METHOD2(setPowerMode, status_t(PhysicalDisplayId, hal::PowerMode));
-    MOCK_METHOD2(setActiveConfig, status_t(HalDisplayId, size_t));
-    MOCK_METHOD2(setColorTransform, status_t(HalDisplayId, const mat4&));
-    MOCK_METHOD1(disconnectDisplay, void(HalDisplayId));
-    MOCK_CONST_METHOD1(hasDeviceComposition, bool(const std::optional<DisplayId>&));
-    MOCK_CONST_METHOD1(getPresentFence, sp<Fence>(HalDisplayId));
-    MOCK_METHOD(nsecs_t, getPresentTimestamp, (PhysicalDisplayId), (const, override));
-    MOCK_CONST_METHOD2(getLayerReleaseFence, sp<Fence>(HalDisplayId, HWC2::Layer*));
-    MOCK_METHOD3(setOutputBuffer,
-                 status_t(HalVirtualDisplayId, const sp<Fence>&, const sp<GraphicBuffer>&));
-    MOCK_METHOD1(clearReleaseFences, void(HalDisplayId));
-    MOCK_METHOD2(getHdrCapabilities, status_t(HalDisplayId, HdrCapabilities*));
-    MOCK_CONST_METHOD1(getSupportedPerFrameMetadata, int32_t(HalDisplayId));
-    MOCK_CONST_METHOD2(getRenderIntents,
-                       std::vector<ui::RenderIntent>(HalDisplayId, ui::ColorMode));
-    MOCK_METHOD2(getDataspaceSaturationMatrix, mat4(HalDisplayId, ui::Dataspace));
-    MOCK_METHOD4(getDisplayedContentSamplingAttributes,
-                 status_t(HalDisplayId, ui::PixelFormat*, ui::Dataspace*, uint8_t*));
-    MOCK_METHOD4(setDisplayContentSamplingEnabled, status_t(HalDisplayId, bool, uint8_t, uint64_t));
-    MOCK_METHOD4(getDisplayedContentSample,
-                 status_t(HalDisplayId, uint64_t, uint64_t, DisplayedFrameStats*));
-    MOCK_METHOD(ftl::Future<status_t>, setDisplayBrightness,
-                (PhysicalDisplayId, float, float, const Hwc2::Composer::DisplayBrightnessOptions&),
-                (override));
-    MOCK_METHOD2(getDisplayBrightnessSupport, status_t(PhysicalDisplayId, bool*));
-
-    MOCK_METHOD2(onHotplug,
-                 std::optional<DisplayIdentificationInfo>(hal::HWDisplayId, hal::Connection));
-    MOCK_CONST_METHOD0(updatesDeviceProductInfoOnHotplugReconnect, bool());
-    MOCK_METHOD(std::optional<PhysicalDisplayId>, onVsync, (hal::HWDisplayId, int64_t));
-    MOCK_METHOD2(setVsyncEnabled, void(PhysicalDisplayId, hal::Vsync));
-    MOCK_CONST_METHOD1(isConnected, bool(PhysicalDisplayId));
-    MOCK_CONST_METHOD2(getModes,
-                       std::vector<HWComposer::HWCDisplayMode>(PhysicalDisplayId, int32_t));
-    MOCK_CONST_METHOD1(getActiveMode, ftl::Expected<hal::HWConfigId, status_t>(PhysicalDisplayId));
-    MOCK_CONST_METHOD1(getColorModes, std::vector<ui::ColorMode>(PhysicalDisplayId));
-    MOCK_METHOD3(setActiveColorMode, status_t(PhysicalDisplayId, ui::ColorMode, ui::RenderIntent));
-    MOCK_CONST_METHOD0(isUsingVrComposer, bool());
-    MOCK_CONST_METHOD1(getDisplayConnectionType, ui::DisplayConnectionType(PhysicalDisplayId));
-    MOCK_CONST_METHOD1(isVsyncPeriodSwitchSupported, bool(PhysicalDisplayId));
-    MOCK_CONST_METHOD1(getDisplayVsyncPeriod, ftl::Expected<nsecs_t, status_t>(PhysicalDisplayId));
-    MOCK_METHOD4(setActiveModeWithConstraints,
-                 status_t(PhysicalDisplayId, hal::HWConfigId,
-                          const hal::VsyncPeriodChangeConstraints&,
-                          hal::VsyncPeriodChangeTimeline*));
-    MOCK_METHOD2(setBootDisplayMode, status_t(PhysicalDisplayId, hal::HWConfigId));
-    MOCK_METHOD1(clearBootDisplayMode, status_t(PhysicalDisplayId));
-    MOCK_METHOD1(getPreferredBootDisplayMode, std::optional<hal::HWConfigId>(PhysicalDisplayId));
-    MOCK_METHOD0(getBootDisplayModeSupport, bool());
-    MOCK_CONST_METHOD0(
-            getHdrConversionCapabilities,
-            std::vector<aidl::android::hardware::graphics::common::HdrConversionCapability>());
-    MOCK_METHOD2(setHdrConversionStrategy,
-                 status_t(aidl::android::hardware::graphics::common::HdrConversionStrategy,
-                          aidl::android::hardware::graphics::common::Hdr*));
-    MOCK_METHOD2(setAutoLowLatencyMode, status_t(PhysicalDisplayId, bool));
-    MOCK_METHOD(status_t, getSupportedContentTypes,
-                (PhysicalDisplayId, std::vector<hal::ContentType>*), (const, override));
-    MOCK_METHOD2(setContentType, status_t(PhysicalDisplayId, hal::ContentType));
-    MOCK_CONST_METHOD0(getSupportedLayerGenericMetadata,
-                       const std::unordered_map<std::string, bool>&());
-
-    MOCK_CONST_METHOD1(dump, void(std::string&));
-    MOCK_CONST_METHOD1(dumpOverlayProperties, void(std::string&));
-    MOCK_CONST_METHOD0(getComposer, android::Hwc2::Composer*());
-
-    MOCK_METHOD(hal::HWDisplayId, getPrimaryHwcDisplayId, (), (const, override));
-    MOCK_METHOD(PhysicalDisplayId, getPrimaryDisplayId, (), (const, override));
-    MOCK_METHOD(bool, isHeadless, (), (const, override));
-
-    MOCK_METHOD(std::optional<PhysicalDisplayId>, toPhysicalDisplayId, (hal::HWDisplayId),
-                (const, override));
-    MOCK_METHOD(std::optional<hal::HWDisplayId>, fromPhysicalDisplayId, (PhysicalDisplayId),
-                (const, override));
-    MOCK_METHOD2(getDisplayDecorationSupport,
-                 status_t(PhysicalDisplayId,
-                          std::optional<aidl::android::hardware::graphics::common::
-                                                DisplayDecorationSupport>* support));
-    MOCK_METHOD2(setIdleTimerEnabled, status_t(PhysicalDisplayId, std::chrono::milliseconds));
-    MOCK_METHOD(bool, hasDisplayIdleTimerCapability, (PhysicalDisplayId), (const, override));
-    MOCK_METHOD(Hwc2::AidlTransform, getPhysicalDisplayOrientation, (PhysicalDisplayId),
-                (const, override));
-    MOCK_METHOD(bool, getValidateSkipped, (HalDisplayId), (const, override));
-    MOCK_METHOD(const aidl::android::hardware::graphics::composer3::OverlayProperties&,
-                getOverlaySupport, (), (const, override));
-    MOCK_METHOD(status_t, setRefreshRateChangedCallbackDebugEnabled, (PhysicalDisplayId, bool));
-    MOCK_METHOD(status_t, notifyExpectedPresent, (PhysicalDisplayId, TimePoint, Fps));
-    MOCK_METHOD((HWC2::Display::LutFileDescriptorMapper&), getLutFileDescriptorMapper, (), ());
-};
-
-} // namespace mock
-} // namespace android
diff --git a/services/surfaceflinger/CompositionEngine/tests/MockPowerAdvisor.cpp b/services/surfaceflinger/CompositionEngine/tests/MockPowerAdvisor.cpp
deleted file mode 100644
index 85b9403..0000000
--- a/services/surfaceflinger/CompositionEngine/tests/MockPowerAdvisor.cpp
+++ /dev/null
@@ -1,34 +0,0 @@
-/*
- * Copyright 2019 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.
- */
-
-#include "MockPowerAdvisor.h"
-
-namespace android {
-namespace Hwc2 {
-
-// This will go away once PowerAdvisor is moved into the "backend" library
-PowerAdvisor::~PowerAdvisor() = default;
-
-namespace mock {
-
-// The Google Mock documentation recommends explicit non-header instantiations
-// for better compile time performance.
-PowerAdvisor::PowerAdvisor() = default;
-PowerAdvisor::~PowerAdvisor() = default;
-
-} // namespace mock
-} // namespace Hwc2
-} // namespace android
diff --git a/services/surfaceflinger/CompositionEngine/tests/MockPowerAdvisor.h b/services/surfaceflinger/CompositionEngine/tests/MockPowerAdvisor.h
deleted file mode 100644
index ed2ffa9..0000000
--- a/services/surfaceflinger/CompositionEngine/tests/MockPowerAdvisor.h
+++ /dev/null
@@ -1,72 +0,0 @@
-/*
- * Copyright 2019 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.
- */
-
-#pragma once
-
-#include <gmock/gmock.h>
-
-#include "DisplayHardware/PowerAdvisor.h"
-
-namespace android {
-namespace Hwc2 {
-namespace mock {
-
-class PowerAdvisor : public android::Hwc2::PowerAdvisor {
-public:
-    PowerAdvisor();
-    ~PowerAdvisor() override;
-
-    MOCK_METHOD(void, init, (), (override));
-    MOCK_METHOD(void, onBootFinished, (), (override));
-    MOCK_METHOD(void, setExpensiveRenderingExpected, (DisplayId displayId, bool expected),
-                (override));
-    MOCK_METHOD(bool, isUsingExpensiveRendering, (), (override));
-    MOCK_METHOD(void, notifyCpuLoadUp, (), (override));
-    MOCK_METHOD(void, notifyDisplayUpdateImminentAndCpuReset, (), (override));
-    MOCK_METHOD(bool, usePowerHintSession, (), (override));
-    MOCK_METHOD(bool, supportsPowerHintSession, (), (override));
-    MOCK_METHOD(bool, supportsGpuReporting, (), (override));
-    MOCK_METHOD(void, updateTargetWorkDuration, (Duration targetDuration), (override));
-    MOCK_METHOD(void, reportActualWorkDuration, (), (override));
-    MOCK_METHOD(void, enablePowerHintSession, (bool enabled), (override));
-    MOCK_METHOD(bool, startPowerHintSession, (std::vector<int32_t> && threadIds), (override));
-    MOCK_METHOD(void, setGpuStartTime, (DisplayId displayId, TimePoint startTime), (override));
-    MOCK_METHOD(void, setGpuFenceTime,
-                (DisplayId displayId, std::unique_ptr<FenceTime>&& fenceTime), (override));
-    MOCK_METHOD(void, setHwcValidateTiming,
-                (DisplayId displayId, TimePoint validateStartTime, TimePoint validateEndTime),
-                (override));
-    MOCK_METHOD(void, setHwcPresentTiming,
-                (DisplayId displayId, TimePoint presentStartTime, TimePoint presentEndTime),
-                (override));
-    MOCK_METHOD(void, setSkippedValidate, (DisplayId displayId, bool skipped), (override));
-    MOCK_METHOD(void, setRequiresRenderEngine, (DisplayId displayId, bool requiresRenderEngine),
-                (override));
-    MOCK_METHOD(void, setExpectedPresentTime, (TimePoint expectedPresentTime), (override));
-    MOCK_METHOD(void, setSfPresentTiming, (TimePoint presentFenceTime, TimePoint presentEndTime),
-                (override));
-    MOCK_METHOD(void, setHwcPresentDelayedTime,
-                (DisplayId displayId, TimePoint earliestFrameStartTime));
-    MOCK_METHOD(void, setFrameDelay, (Duration frameDelayDuration), (override));
-    MOCK_METHOD(void, setCommitStart, (TimePoint commitStartTime), (override));
-    MOCK_METHOD(void, setCompositeEnd, (TimePoint compositeEndTime), (override));
-    MOCK_METHOD(void, setDisplays, (std::vector<DisplayId> & displayIds), (override));
-    MOCK_METHOD(void, setTotalFrameTargetWorkDuration, (Duration targetDuration), (override));
-};
-
-} // namespace mock
-} // namespace Hwc2
-} // namespace android
diff --git a/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp b/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
index b21533a..f2c5672 100644
--- a/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/OutputLayerTest.cpp
@@ -23,14 +23,14 @@
 #include <compositionengine/mock/Output.h>
 #include <gtest/gtest.h>
 #include <log/log.h>
-
 #include <renderengine/impl/ExternalTexture.h>
 #include <renderengine/mock/RenderEngine.h>
+#include <ui/FloatRect.h>
 #include <ui/PixelFormat.h>
-#include "MockHWC2.h"
-#include "MockHWComposer.h"
+
 #include "RegionMatcher.h"
-#include "ui/FloatRect.h"
+#include "mock/DisplayHardware/MockHWC2.h"
+#include "mock/DisplayHardware/MockHWComposer.h"
 
 #include <aidl/android/hardware/graphics/composer3/Composition.h>
 
diff --git a/services/surfaceflinger/CompositionEngine/tests/OutputTest.cpp b/services/surfaceflinger/CompositionEngine/tests/OutputTest.cpp
index 74ff124..fe7dd9a 100644
--- a/services/surfaceflinger/CompositionEngine/tests/OutputTest.cpp
+++ b/services/surfaceflinger/CompositionEngine/tests/OutputTest.cpp
@@ -40,8 +40,8 @@
 #include <common/FlagManager.h>
 #include <common/test/FlagUtils.h>
 #include "CallOrderStateMachineHelper.h"
-#include "MockHWC2.h"
 #include "RegionMatcher.h"
+#include "mock/DisplayHardware/MockHWC2.h"
 
 namespace android::compositionengine {
 namespace {
diff --git a/services/surfaceflinger/fuzzer/Android.bp b/services/surfaceflinger/fuzzer/Android.bp
index ae502cf..3582d38 100644
--- a/services/surfaceflinger/fuzzer/Android.bp
+++ b/services/surfaceflinger/fuzzer/Android.bp
@@ -32,12 +32,15 @@
         "libsurfaceflinger_common",
     ],
     srcs: [
+        ":libsurfaceflinger_backend_mock_sources",
+        ":libsurfaceflinger_mock_sources",
         ":libsurfaceflinger_sources",
     ],
     defaults: [
         "libsurfaceflinger_defaults",
     ],
     header_libs: [
+        "libsurfaceflinger_backend_mock_headers",
         "libsurfaceflinger_headers",
     ],
     cflags: [
diff --git a/services/surfaceflinger/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index 40a6fb8..8269fcb 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -22,15 +22,40 @@
     default_team: "trendy_team_android_core_graphics_stack",
 }
 
+// This is a step towards pulling out the "backend" sources to clean up the
+// dependency graph between CompositionEngine and SurfaceFlinger.
+// MockNativeWindow doesn't strictly belong here, but this works for now so
+// that CompositionEngine tests can use these mocks.
 filegroup {
-    name: "libsurfaceflinger_mock_sources",
+    name: "libsurfaceflinger_backend_mock_sources",
     srcs: [
-        "mock/DisplayHardware/MockPowerHalController.cpp",
         "mock/DisplayHardware/MockComposer.cpp",
         "mock/DisplayHardware/MockHWC2.cpp",
+        "mock/DisplayHardware/MockHWComposer.cpp",
         "mock/DisplayHardware/MockIPower.cpp",
         "mock/DisplayHardware/MockPowerHintSessionWrapper.cpp",
         "mock/DisplayHardware/MockPowerAdvisor.cpp",
+        "mock/DisplayHardware/MockPowerHalController.cpp",
+        "mock/system/window/MockNativeWindow.cpp",
+    ],
+}
+
+cc_library_headers {
+    name: "libsurfaceflinger_backend_mock_headers",
+    export_include_dirs: ["."],
+    static_libs: [
+        "libgmock",
+        "libgtest",
+    ],
+    export_static_lib_headers: [
+        "libgmock",
+        "libgtest",
+    ],
+}
+
+filegroup {
+    name: "libsurfaceflinger_mock_sources",
+    srcs: [
         "mock/MockEventThread.cpp",
         "mock/MockFrameTimeline.cpp",
         "mock/MockFrameTracer.cpp",
@@ -39,7 +64,6 @@
         "mock/MockVsyncController.cpp",
         "mock/MockVSyncDispatch.cpp",
         "mock/MockVSyncTracker.cpp",
-        "mock/system/window/MockNativeWindow.cpp",
     ],
 }
 
@@ -60,6 +84,7 @@
     static_libs: ["libc++fs"],
     header_libs: ["surfaceflinger_tests_common_headers"],
     srcs: [
+        ":libsurfaceflinger_backend_mock_sources",
         ":libsurfaceflinger_mock_sources",
         ":libsurfaceflinger_sources",
         "libsurfaceflinger_unittest_main.cpp",
diff --git a/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWC2.h b/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWC2.h
index 384b908..121104d 100644
--- a/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWC2.h
+++ b/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWC2.h
@@ -126,6 +126,8 @@
                 (uint32_t, const android::sp<android::GraphicBuffer> &,
                  const android::sp<android::Fence> &),
                 (override));
+    MOCK_METHOD(hal::Error, setBufferSlotsToClear,
+                (const std::vector<uint32_t>& slotsToClear, uint32_t activeBufferSlot), (override));
     MOCK_METHOD(hal::Error, setSurfaceDamage, (const android::Region &), (override));
     MOCK_METHOD(hal::Error, setBlendMode, (hal::BlendMode), (override));
     MOCK_METHOD(hal::Error, setColor, (aidl::android::hardware::graphics::composer3::Color),
diff --git a/services/surfaceflinger/CompositionEngine/tests/MockHWComposer.cpp b/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWComposer.cpp
similarity index 81%
rename from services/surfaceflinger/CompositionEngine/tests/MockHWComposer.cpp
rename to services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWComposer.cpp
index ae52670..f310633 100644
--- a/services/surfaceflinger/CompositionEngine/tests/MockHWComposer.cpp
+++ b/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWComposer.cpp
@@ -16,17 +16,11 @@
 
 #include "MockHWComposer.h"
 
-namespace android {
-
-// This will go away once HWComposer is moved into the "backend" library
-HWComposer::~HWComposer() = default;
-
-namespace mock {
+namespace android::mock {
 
 // The Google Mock documentation recommends explicit non-header instantiations
 // for better compile time performance.
 HWComposer::HWComposer() = default;
 HWComposer::~HWComposer() = default;
 
-} // namespace mock
-} // namespace android
+} // namespace android::mock
diff --git a/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWComposer.h b/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWComposer.h
new file mode 100644
index 0000000..fa7128c
--- /dev/null
+++ b/services/surfaceflinger/tests/unittests/mock/DisplayHardware/MockHWComposer.h
@@ -0,0 +1,153 @@
+/*
+ * Copyright 2024 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.
+ */
+
+#pragma once
+
+#include <gmock/gmock.h>
+
+#include "DisplayHardware/HWComposer.h"
+
+namespace android::mock {
+
+class HWComposer : public android::HWComposer {
+public:
+    using HWDisplayId = android::hardware::graphics::composer::hal::HWDisplayId;
+    using PowerMode = android::hardware::graphics::composer::hal::PowerMode;
+
+    HWComposer();
+    ~HWComposer() override;
+
+    MOCK_METHOD(void, setCallback, (HWC2::ComposerCallback&), (override));
+    MOCK_METHOD(bool, getDisplayIdentificationData,
+                (HWDisplayId, uint8_t*, DisplayIdentificationData*), (const, override));
+    MOCK_METHOD(bool, hasCapability, (aidl::android::hardware::graphics::composer3::Capability),
+                (const, override));
+    MOCK_METHOD(bool, hasDisplayCapability,
+                (HalDisplayId, aidl::android::hardware::graphics::composer3::DisplayCapability),
+                (const, override));
+
+    MOCK_METHOD(size_t, getMaxVirtualDisplayCount, (), (const, override));
+    MOCK_METHOD(size_t, getMaxVirtualDisplayDimension, (), (const, override));
+    MOCK_METHOD(bool, allocateVirtualDisplay, (HalVirtualDisplayId, ui::Size, ui::PixelFormat*),
+                (override));
+    MOCK_METHOD(void, allocatePhysicalDisplay,
+                (hal::HWDisplayId, PhysicalDisplayId, std::optional<ui::Size>), (override));
+
+    MOCK_METHOD(std::shared_ptr<HWC2::Layer>, createLayer, (HalDisplayId), (override));
+    MOCK_METHOD(status_t, getDeviceCompositionChanges,
+                (HalDisplayId, bool, std::optional<std::chrono::steady_clock::time_point>, nsecs_t,
+                 Fps, std::optional<android::HWComposer::DeviceRequestedChanges>*));
+    MOCK_METHOD(status_t, setClientTarget,
+                (HalDisplayId, uint32_t, const sp<Fence>&, const sp<GraphicBuffer>&, ui::Dataspace,
+                 float),
+                (override));
+    MOCK_METHOD(status_t, presentAndGetReleaseFences,
+                (HalDisplayId, std::optional<std::chrono::steady_clock::time_point>), (override));
+    MOCK_METHOD(status_t, executeCommands, (HalDisplayId));
+    MOCK_METHOD(status_t, setPowerMode, (PhysicalDisplayId, PowerMode), (override));
+    MOCK_METHOD(status_t, setColorTransform, (HalDisplayId, const mat4&), (override));
+    MOCK_METHOD(void, disconnectDisplay, (HalDisplayId), (override));
+    MOCK_METHOD(sp<Fence>, getPresentFence, (HalDisplayId), (const, override));
+    MOCK_METHOD(nsecs_t, getPresentTimestamp, (PhysicalDisplayId), (const, override));
+    MOCK_METHOD(sp<Fence>, getLayerReleaseFence, (HalDisplayId, HWC2::Layer*), (const, override));
+    MOCK_METHOD(status_t, setOutputBuffer,
+                (HalVirtualDisplayId, const sp<Fence>&, const sp<GraphicBuffer>&), (override));
+    MOCK_METHOD(void, clearReleaseFences, (HalDisplayId), (override));
+    MOCK_METHOD(status_t, getHdrCapabilities, (HalDisplayId, HdrCapabilities*), (override));
+    MOCK_METHOD(int32_t, getSupportedPerFrameMetadata, (HalDisplayId), (const, override));
+    MOCK_METHOD(std::vector<ui::RenderIntent>, getRenderIntents, (HalDisplayId, ui::ColorMode),
+                (const, override));
+    MOCK_METHOD(mat4, getDataspaceSaturationMatrix, (HalDisplayId, ui::Dataspace), (override));
+    MOCK_METHOD(status_t, getDisplayedContentSamplingAttributes,
+                (HalDisplayId, ui::PixelFormat*, ui::Dataspace*, uint8_t*), (override));
+    MOCK_METHOD(status_t, setDisplayContentSamplingEnabled, (HalDisplayId, bool, uint8_t, uint64_t),
+                (override));
+    MOCK_METHOD(status_t, getDisplayedContentSample,
+                (HalDisplayId, uint64_t, uint64_t, DisplayedFrameStats*), (override));
+    MOCK_METHOD(ftl::Future<status_t>, setDisplayBrightness,
+                (PhysicalDisplayId, float, float, const Hwc2::Composer::DisplayBrightnessOptions&),
+                (override));
+    MOCK_METHOD(std::optional<DisplayIdentificationInfo>, onHotplug,
+                (hal::HWDisplayId, hal::Connection), (override));
+    MOCK_METHOD(bool, updatesDeviceProductInfoOnHotplugReconnect, (), (const, override));
+    MOCK_METHOD(std::optional<PhysicalDisplayId>, onVsync, (hal::HWDisplayId, int64_t));
+    MOCK_METHOD(void, setVsyncEnabled, (PhysicalDisplayId, hal::Vsync), (override));
+    MOCK_METHOD(bool, isConnected, (PhysicalDisplayId), (const, override));
+    MOCK_METHOD(std::vector<HWComposer::HWCDisplayMode>, getModes, (PhysicalDisplayId, int32_t),
+                (const, override));
+    MOCK_METHOD((ftl::Expected<hal::HWConfigId, status_t>), getActiveMode, (PhysicalDisplayId),
+                (const, override));
+    MOCK_METHOD(std::vector<ui::ColorMode>, getColorModes, (PhysicalDisplayId), (const, override));
+    MOCK_METHOD(status_t, setActiveColorMode, (PhysicalDisplayId, ui::ColorMode, ui::RenderIntent),
+                (override));
+    MOCK_METHOD(ui::DisplayConnectionType, getDisplayConnectionType, (PhysicalDisplayId),
+                (const, override));
+    MOCK_METHOD(bool, isVsyncPeriodSwitchSupported, (PhysicalDisplayId), (const, override));
+    MOCK_METHOD((ftl::Expected<nsecs_t, status_t>), getDisplayVsyncPeriod, (PhysicalDisplayId),
+                (const, override));
+    MOCK_METHOD(status_t, setActiveModeWithConstraints,
+                (PhysicalDisplayId, hal::HWConfigId, const hal::VsyncPeriodChangeConstraints&,
+                 hal::VsyncPeriodChangeTimeline*),
+                (override));
+    MOCK_METHOD(status_t, setBootDisplayMode, (PhysicalDisplayId, hal::HWConfigId), (override));
+    MOCK_METHOD(status_t, clearBootDisplayMode, (PhysicalDisplayId), (override));
+    MOCK_METHOD(std::optional<hal::HWConfigId>, getPreferredBootDisplayMode, (PhysicalDisplayId),
+                (override));
+
+    MOCK_METHOD(std::vector<aidl::android::hardware::graphics::common::HdrConversionCapability>,
+                getHdrConversionCapabilities, (), (const, override));
+    MOCK_METHOD(status_t, setHdrConversionStrategy,
+                (aidl::android::hardware::graphics::common::HdrConversionStrategy,
+                 aidl::android::hardware::graphics::common::Hdr*),
+                (override));
+    MOCK_METHOD(status_t, setAutoLowLatencyMode, (PhysicalDisplayId, bool), (override));
+    MOCK_METHOD(status_t, getSupportedContentTypes,
+                (PhysicalDisplayId, std::vector<hal::ContentType>*), (const, override));
+    MOCK_METHOD(status_t, setContentType, (PhysicalDisplayId, hal::ContentType)), (override);
+    MOCK_METHOD((const std::unordered_map<std::string, bool>&), getSupportedLayerGenericMetadata,
+                (), (const, override));
+    MOCK_METHOD(void, dump, (std::string&), (const, override));
+    MOCK_METHOD(void, dumpOverlayProperties, (std::string&), (const, override));
+    MOCK_METHOD(android::Hwc2::Composer*, getComposer, (), (const, override));
+
+    MOCK_METHOD(hal::HWDisplayId, getPrimaryHwcDisplayId, (), (const, override));
+    MOCK_METHOD(PhysicalDisplayId, getPrimaryDisplayId, (), (const, override));
+    MOCK_METHOD(bool, isHeadless, (), (const, override));
+
+    MOCK_METHOD(std::optional<PhysicalDisplayId>, toPhysicalDisplayId, (hal::HWDisplayId),
+                (const, override));
+    MOCK_METHOD(std::optional<hal::HWDisplayId>, fromPhysicalDisplayId, (PhysicalDisplayId),
+                (const, override));
+    MOCK_METHOD(status_t, getDisplayDecorationSupport,
+                (PhysicalDisplayId,
+                 std::optional<aidl::android::hardware::graphics::common::DisplayDecorationSupport>*
+                         support),
+                (override));
+    MOCK_METHOD(status_t, setIdleTimerEnabled, (PhysicalDisplayId, std::chrono::milliseconds),
+                (override));
+    MOCK_METHOD(bool, hasDisplayIdleTimerCapability, (PhysicalDisplayId), (const, override));
+    MOCK_METHOD(Hwc2::AidlTransform, getPhysicalDisplayOrientation, (PhysicalDisplayId),
+                (const, override));
+    MOCK_METHOD(bool, getValidateSkipped, (HalDisplayId), (const, override));
+    MOCK_METHOD(const aidl::android::hardware::graphics::composer3::OverlayProperties&,
+                getOverlaySupport, (), (const, override));
+    MOCK_METHOD(status_t, setRefreshRateChangedCallbackDebugEnabled, (PhysicalDisplayId, bool));
+    MOCK_METHOD(status_t, notifyExpectedPresent, (PhysicalDisplayId, TimePoint, Fps));
+    MOCK_METHOD(HWC2::Display::LutFileDescriptorMapper&, getLutFileDescriptorMapper, (),
+                (override));
+};
+
+} // namespace android::mock