SF: Flow DisplayModeRequest through mode set FSM

The motivation is to:
    - Avoid redundant state that can cause data races if stale.
    - Consolidate control flow for resolution and refresh rate changes.
    - Clarify the desired/pending/active states of the per-display FSM.

The notable changes are:

Consume the desired DisplayModeRequestOpt via either SF::dropModeRequest
or DisplayDevice::initiateModeChange.

Pull the details of SF::finalizeDisplayModeChange into DisplayDevice::
finalizeModeChange, which now returns whether there was NoModeChange,
a ResolutionChange, or a RefreshRateChange. Consume the pending request.

Now that DisplayDevice does not retain the desired DisplayModeRequest,
applyActiveMode as soon as finalizeDisplayModeChange ends, rather than
at a later point in the commit, when initiateDisplayModeChanges checks
whether the active and desired modes are the same.

Now that applyActiveMode happens in finalizeDisplayModeChange, remove
the special case when there is a displayToUpdateImmediately.

Bug: 305813445
Bug: 255635711
Bug: 241285876
Test: ALOGV of mode setting for inner/outer displays
Test: InitiateModeChangeTest, DisplayModeSwitchingTest
Change-Id: I688b0c922747a80e881965a1dc243d11ba2c7438
diff --git a/services/surfaceflinger/DisplayDevice.cpp b/services/surfaceflinger/DisplayDevice.cpp
index 950b05e..671382c 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -222,7 +222,6 @@
                                        const hal::VsyncPeriodChangeConstraints& constraints,
                                        hal::VsyncPeriodChangeTimeline& outTimeline) {
     mPendingModeOpt = std::move(desiredMode);
-    mIsModeSetPending = true;
 
     const auto& mode = *mPendingModeOpt->mode.modePtr;
 
@@ -235,9 +234,22 @@
     return true;
 }
 
-void DisplayDevice::finalizeModeChange(DisplayModeId modeId, Fps vsyncRate, Fps renderFps) {
-    setActiveMode(modeId, vsyncRate, renderFps);
-    mIsModeSetPending = false;
+auto DisplayDevice::finalizeModeChange() -> ModeChange {
+    if (!mPendingModeOpt) return NoModeChange{"No pending mode"};
+
+    auto pendingMode = *std::exchange(mPendingModeOpt, std::nullopt);
+    auto& pendingModePtr = pendingMode.mode.modePtr;
+
+    if (!mRefreshRateSelector->displayModes().contains(pendingModePtr->getId())) {
+        return NoModeChange{"Unknown pending mode"};
+    }
+
+    if (getActiveMode().modePtr->getResolution() != pendingModePtr->getResolution()) {
+        return ResolutionChange{std::move(pendingMode)};
+    }
+
+    setActiveMode(pendingModePtr->getId(), pendingModePtr->getVsyncRate(), pendingMode.mode.fps);
+    return RefreshRateChange{std::move(pendingMode)};
 }
 
 nsecs_t DisplayDevice::getVsyncPeriodFromHWC() const {
@@ -571,10 +583,14 @@
     return mDesiredModeOpt;
 }
 
-void DisplayDevice::clearDesiredMode() {
-    std::scoped_lock lock(mDesiredModeLock);
-    mDesiredModeOpt.reset();
-    mHasDesiredModeTrace = false;
+auto DisplayDevice::takeDesiredMode() -> DisplayModeRequestOpt {
+    DisplayModeRequestOpt desiredModeOpt;
+    {
+        std::scoped_lock lock(mDesiredModeLock);
+        std::swap(mDesiredModeOpt, desiredModeOpt);
+        mHasDesiredModeTrace = false;
+    }
+    return desiredModeOpt;
 }
 
 void DisplayDevice::adjustRefreshRate(Fps pacesetterDisplayRefreshRate) {
diff --git a/services/surfaceflinger/DisplayDevice.h b/services/surfaceflinger/DisplayDevice.h
index ac390cb..3090477 100644
--- a/services/surfaceflinger/DisplayDevice.h
+++ b/services/surfaceflinger/DisplayDevice.h
@@ -19,6 +19,7 @@
 #include <memory>
 #include <string>
 #include <unordered_map>
+#include <variant>
 
 #include <android-base/thread_annotations.h>
 #include <android/native_window.h>
@@ -194,12 +195,11 @@
     using DisplayModeRequestOpt = ftl::Optional<display::DisplayModeRequest>;
 
     DisplayModeRequestOpt getDesiredMode() const EXCLUDES(mDesiredModeLock);
-    void clearDesiredMode() EXCLUDES(mDesiredModeLock);
+    DisplayModeRequestOpt takeDesiredMode() EXCLUDES(mDesiredModeLock);
 
-    DisplayModeRequestOpt getPendingMode() const REQUIRES(kMainThreadContext) {
-        return mPendingModeOpt;
+    bool isModeSetPending() const REQUIRES(kMainThreadContext) {
+        return mPendingModeOpt.has_value();
     }
-    bool isModeSetPending() const REQUIRES(kMainThreadContext) { return mIsModeSetPending; }
 
     scheduler::FrameRateMode getActiveMode() const REQUIRES(kMainThreadContext) {
         return mRefreshRateSelector->getActiveMode();
@@ -211,8 +211,25 @@
                             hal::VsyncPeriodChangeTimeline& outTimeline)
             REQUIRES(kMainThreadContext);
 
-    void finalizeModeChange(DisplayModeId, Fps vsyncRate, Fps renderFps)
-            REQUIRES(kMainThreadContext);
+    struct NoModeChange {
+        const char* reason;
+    };
+
+    struct ResolutionChange {
+        display::DisplayModeRequest activeMode;
+    };
+
+    struct RefreshRateChange {
+        display::DisplayModeRequest activeMode;
+    };
+
+    using ModeChange = std::variant<NoModeChange, ResolutionChange, RefreshRateChange>;
+
+    // Clears the pending DisplayModeRequest, and returns the ModeChange that occurred. If it was a
+    // RefreshRateChange, the pending mode becomes the active mode. If it was a ResolutionChange,
+    // the caller is responsible for resizing the framebuffer to match the active resolution by
+    // recreating the DisplayDevice.
+    ModeChange finalizeModeChange() REQUIRES(kMainThreadContext);
 
     scheduler::RefreshRateSelector& refreshRateSelector() const { return *mRefreshRateSelector; }
 
@@ -249,6 +266,8 @@
     void dump(utils::Dumper&) const;
 
 private:
+    friend class TestableSurfaceFlinger;
+
     template <size_t N>
     inline std::string concatId(const char (&str)[N]) const {
         return std::string(ftl::Concat(str, ' ', getId().value).str());
@@ -299,12 +318,15 @@
     // This parameter is only used for hdr/sdr ratio overlay
     float mHdrSdrRatio = 1.0f;
 
+    // A DisplayModeRequest flows through three states: desired, pending, and active. Requests
+    // within a frame are merged into a single desired request. Unless cleared, the request is
+    // relayed to HWC on the next frame, and becomes pending. The mode becomes active once HWC
+    // signals the present fence to confirm the mode set.
     mutable std::mutex mDesiredModeLock;
     DisplayModeRequestOpt mDesiredModeOpt GUARDED_BY(mDesiredModeLock);
     TracedOrdinal<bool> mHasDesiredModeTrace GUARDED_BY(mDesiredModeLock);
 
     DisplayModeRequestOpt mPendingModeOpt GUARDED_BY(kMainThreadContext);
-    bool mIsModeSetPending GUARDED_BY(kMainThreadContext) = false;
 };
 
 struct DisplayDeviceState {
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 2769e5d..7230547 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -59,6 +59,7 @@
 #include <ftl/concat.h>
 #include <ftl/fake_guard.h>
 #include <ftl/future.h>
+#include <ftl/match.h>
 #include <ftl/unit.h>
 #include <gui/AidlStatusUtil.h>
 #include <gui/BufferQueue.h>
@@ -1229,20 +1230,21 @@
     return NO_ERROR;
 }
 
-void SurfaceFlinger::setDesiredMode(display::DisplayModeRequest&& request, bool force) {
-    const auto displayId = request.mode.modePtr->getPhysicalDisplayId();
+void SurfaceFlinger::setDesiredMode(display::DisplayModeRequest&& desiredMode, bool force) {
+    const auto mode = desiredMode.mode;
+    const auto displayId = mode.modePtr->getPhysicalDisplayId();
+
     ATRACE_NAME(ftl::Concat(__func__, ' ', displayId.value).c_str());
 
     const auto display = getDisplayDeviceLocked(displayId);
     if (!display) {
-        ALOGW("%s: display is no longer valid", __func__);
+        ALOGW("%s: Unknown display %s", __func__, to_string(displayId).c_str());
         return;
     }
 
-    const auto mode = request.mode;
-    const bool emitEvent = request.emitEvent;
+    const bool emitEvent = desiredMode.emitEvent;
 
-    switch (display->setDesiredMode(std::move(request), force)) {
+    switch (display->setDesiredMode(std::move(desiredMode), force)) {
         case DisplayDevice::DesiredModeAction::InitiateDisplayModeSwitch:
             // DisplayDevice::setDesiredMode updated the render rate, so inform Scheduler.
             mScheduler->setRenderRate(displayId,
@@ -1338,61 +1340,55 @@
     const auto displayId = display.getPhysicalId();
     ATRACE_NAME(ftl::Concat(__func__, ' ', displayId.value).c_str());
 
-    const auto pendingModeOpt = display.getPendingMode();
-    if (!pendingModeOpt) {
-        // There is no pending mode change. This can happen if the active
-        // display changed and the mode change happened on a different display.
-        return;
-    }
+    ftl::match(
+            display.finalizeModeChange(),
+            [this, displayId](DisplayDevice::RefreshRateChange change) {
+                ftl::FakeGuard guard(mStateLock);
 
-    const auto& activeMode = pendingModeOpt->mode;
+                if (change.activeMode.emitEvent) {
+                    dispatchDisplayModeChangeEvent(displayId, change.activeMode.mode);
+                }
 
-    if (display.getActiveMode().modePtr->getResolution() != activeMode.modePtr->getResolution()) {
-        auto& state = mCurrentState.displays.editValueFor(display.getDisplayToken());
-        // We need to generate new sequenceId in order to recreate the display (and this
-        // way the framebuffer).
-        state.sequenceId = DisplayDeviceState{}.sequenceId;
-        state.physical->activeMode = activeMode.modePtr.get();
-        processDisplayChangesLocked();
+                applyActiveMode(std::move(change.activeMode));
+            },
+            [&](DisplayDevice::ResolutionChange change) {
+                auto& state = mCurrentState.displays.editValueFor(display.getDisplayToken());
+                // Assign a new sequence ID to recreate the display and so its framebuffer.
+                state.sequenceId = DisplayDeviceState{}.sequenceId;
+                state.physical->activeMode = change.activeMode.mode.modePtr.get();
 
-        // processDisplayChangesLocked will update all necessary components so we're done here.
-        return;
-    }
+                ftl::FakeGuard guard1(kMainThreadContext);
+                ftl::FakeGuard guard2(mStateLock);
+                processDisplayChangesLocked();
 
-    display.finalizeModeChange(activeMode.modePtr->getId(), activeMode.modePtr->getVsyncRate(),
-                               activeMode.fps);
-
-    if (displayId == mActiveDisplayId) {
-        mRefreshRateStats->setRefreshRate(activeMode.fps);
-        updatePhaseConfiguration(activeMode.fps);
-    }
-
-    if (pendingModeOpt->emitEvent) {
-        dispatchDisplayModeChangeEvent(displayId, activeMode);
-    }
+                applyActiveMode(std::move(change.activeMode));
+            },
+            [](DisplayDevice::NoModeChange noChange) {
+                // TODO(b/255635821): Remove this case, as it should no longer happen.
+                ALOGE("A mode change was initiated but not finalized: %s", noChange.reason);
+            });
 }
 
-void SurfaceFlinger::dropModeRequest(const sp<DisplayDevice>& display) {
-    display->clearDesiredMode();
-    if (display->getPhysicalId() == mActiveDisplayId) {
+void SurfaceFlinger::dropModeRequest(display::DisplayModeRequest&& request) {
+    if (request.mode.modePtr->getPhysicalDisplayId() == mActiveDisplayId) {
         // TODO(b/255635711): Check for pending mode changes on other displays.
         mScheduler->setModeChangePending(false);
     }
 }
 
-void SurfaceFlinger::applyActiveMode(const sp<DisplayDevice>& display) {
-    const auto activeModeOpt = display->getDesiredMode();
-    auto activeModePtr = activeModeOpt->mode.modePtr;
+void SurfaceFlinger::applyActiveMode(display::DisplayModeRequest&& activeMode) {
+    auto activeModePtr = activeMode.mode.modePtr;
     const auto displayId = activeModePtr->getPhysicalDisplayId();
-    const auto renderFps = activeModeOpt->mode.fps;
+    const auto renderFps = activeMode.mode.fps;
 
-    dropModeRequest(display);
+    dropModeRequest(std::move(activeMode));
 
     constexpr bool kAllowToEnable = true;
     mScheduler->resyncToHardwareVsync(displayId, kAllowToEnable, std::move(activeModePtr).take());
     mScheduler->setRenderRate(displayId, renderFps);
 
     if (displayId == mActiveDisplayId) {
+        mRefreshRateStats->setRefreshRate(renderFps);
         updatePhaseConfiguration(renderFps);
     }
 }
@@ -1406,50 +1402,50 @@
         const auto display = getDisplayDeviceLocked(id);
         if (!display) continue;
 
-        auto desiredModeOpt = display->getDesiredMode();
+        auto desiredModeOpt = display->takeDesiredMode();
         if (!desiredModeOpt) {
             continue;
         }
 
+        auto desiredMode = std::move(*desiredModeOpt);
+
         if (!shouldApplyRefreshRateSelectorPolicy(*display)) {
-            dropModeRequest(display);
+            dropModeRequest(std::move(desiredMode));
             continue;
         }
 
-        const auto desiredModeId = desiredModeOpt->mode.modePtr->getId();
+        const auto desiredModeId = desiredMode.mode.modePtr->getId();
         const auto displayModePtrOpt = physical.snapshot().displayModes().get(desiredModeId);
 
         if (!displayModePtrOpt) {
-            ALOGW("Desired display mode is no longer supported. Mode ID = %d",
-                  desiredModeId.value());
-            dropModeRequest(display);
+            ALOGW("%s: Unknown mode %d for display %s", __func__, desiredModeId.value(),
+                  to_string(id).c_str());
+            dropModeRequest(std::move(desiredMode));
             continue;
         }
 
-        ALOGV("%s changing active mode to %d(%s) for display %s", __func__, desiredModeId.value(),
-              to_string(displayModePtrOpt->get()->getVsyncRate()).c_str(),
-              to_string(display->getId()).c_str());
-
-        if (display->getActiveMode() == desiredModeOpt->mode) {
-            applyActiveMode(display);
+        if (display->getActiveMode() == desiredMode.mode) {
+            dropModeRequest(std::move(desiredMode));
             continue;
         }
 
-        // Desired active mode was set, it is different than the mode currently in use, however
-        // allowed modes might have changed by the time we process the refresh.
-        // Make sure the desired mode is still allowed
-        if (!display->refreshRateSelector().isModeAllowed(desiredModeOpt->mode)) {
-            dropModeRequest(display);
+        // The desired mode is different from the active mode. However, the allowed modes might have
+        // changed since setDesiredMode scheduled a mode transition.
+        if (!display->refreshRateSelector().isModeAllowed(desiredMode.mode)) {
+            dropModeRequest(std::move(desiredMode));
             continue;
         }
 
-        // TODO(b/142753666) use constrains
+        ALOGV("Mode setting display %s to %d (%s)", to_string(id).c_str(), desiredModeId.value(),
+              to_string(displayModePtrOpt.value().get()->getVsyncRate()).c_str());
+
+        // TODO(b/142753666): Use constraints.
         hal::VsyncPeriodChangeConstraints constraints;
         constraints.desiredTimeNanos = systemTime();
         constraints.seamlessRequired = false;
         hal::VsyncPeriodChangeTimeline outTimeline;
 
-        if (!display->initiateModeChange(std::move(*desiredModeOpt), constraints, outTimeline)) {
+        if (!display->initiateModeChange(std::move(desiredMode), constraints, outTimeline)) {
             continue;
         }
 
@@ -1469,11 +1465,6 @@
     if (displayToUpdateImmediately) {
         const auto display = getDisplayDeviceLocked(*displayToUpdateImmediately);
         finalizeDisplayModeChange(*display);
-
-        const auto desiredModeOpt = display->getDesiredMode();
-        if (desiredModeOpt && display->getActiveMode() == desiredModeOpt->mode) {
-            applyActiveMode(display);
-        }
     }
 }
 
@@ -7391,7 +7382,7 @@
     if (!updateOverlay) return;
 
     // Update the overlay on the main thread to avoid race conditions with
-    // RefreshRateSelector::getActiveMode
+    // RefreshRateSelector::getActiveMode.
     static_cast<void>(mScheduler->schedule([=, this] {
         const auto display = FTL_FAKE_GUARD(mStateLock, getDefaultDisplayDeviceLocked());
         if (!display) {
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 6b44401..d2db685 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -725,9 +725,9 @@
     void initiateDisplayModeChanges() REQUIRES(mStateLock, kMainThreadContext);
     void finalizeDisplayModeChange(DisplayDevice&) REQUIRES(mStateLock, kMainThreadContext);
 
-    // TODO(b/241285191): Replace DisplayDevice with DisplayModeRequest, and move to Scheduler.
-    void dropModeRequest(const sp<DisplayDevice>&) REQUIRES(mStateLock);
-    void applyActiveMode(const sp<DisplayDevice>&) REQUIRES(mStateLock);
+    // TODO(b/241285191): Move to Scheduler.
+    void dropModeRequest(display::DisplayModeRequest&&) REQUIRES(mStateLock);
+    void applyActiveMode(display::DisplayModeRequest&&) REQUIRES(mStateLock);
 
     // Called on the main thread in response to setPowerMode()
     void setPowerModeInternal(const sp<DisplayDevice>& display, hal::PowerMode mode)
diff --git a/services/surfaceflinger/tests/unittests/DisplayDevice_InitiateModeChange.cpp b/services/surfaceflinger/tests/unittests/DisplayDevice_InitiateModeChange.cpp
index c463a92..220001b 100644
--- a/services/surfaceflinger/tests/unittests/DisplayDevice_InitiateModeChange.cpp
+++ b/services/surfaceflinger/tests/unittests/DisplayDevice_InitiateModeChange.cpp
@@ -23,10 +23,13 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
-#define EXPECT_DISPLAY_MODE_REQUEST(expected, requestOpt)                               \
-    ASSERT_TRUE(requestOpt);                                                            \
-    EXPECT_FRAME_RATE_MODE(expected.mode.modePtr, expected.mode.fps, requestOpt->mode); \
-    EXPECT_EQ(expected.emitEvent, requestOpt->emitEvent)
+#define EXPECT_DISPLAY_MODE_REQUEST(expected, request)                              \
+    EXPECT_FRAME_RATE_MODE(expected.mode.modePtr, expected.mode.fps, request.mode); \
+    EXPECT_EQ(expected.emitEvent, request.emitEvent)
+
+#define EXPECT_DISPLAY_MODE_REQUEST_OPT(expected, requestOpt) \
+    ASSERT_TRUE(requestOpt);                                  \
+    EXPECT_DISPLAY_MODE_REQUEST(expected, (*requestOpt))
 
 namespace android {
 namespace {
@@ -37,6 +40,7 @@
 class InitiateModeChangeTest : public DisplayTransactionTest {
 public:
     using Action = DisplayDevice::DesiredModeAction;
+
     void SetUp() override {
         injectFakeBufferQueueFactory();
         injectFakeNativeWindowSurfaceFactory();
@@ -84,36 +88,43 @@
 TEST_F(InitiateModeChangeTest, setDesiredMode) {
     EXPECT_EQ(Action::InitiateDisplayModeSwitch,
               mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode90)));
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, mDisplay->getDesiredMode());
+    EXPECT_DISPLAY_MODE_REQUEST_OPT(kDesiredMode90, mDisplay->getDesiredMode());
 
     EXPECT_EQ(Action::None, mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode120)));
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode120, mDisplay->getDesiredMode());
+    EXPECT_DISPLAY_MODE_REQUEST_OPT(kDesiredMode120, mDisplay->getDesiredMode());
 }
 
-TEST_F(InitiateModeChangeTest, clearDesiredMode) {
+TEST_F(InitiateModeChangeTest, takeDesiredMode) {
     EXPECT_EQ(Action::InitiateDisplayModeSwitch,
               mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode90)));
-    EXPECT_TRUE(mDisplay->getDesiredMode());
+    EXPECT_EQ(kDesiredMode90, mDisplay->getDesiredMode());
 
-    mDisplay->clearDesiredMode();
+    EXPECT_EQ(kDesiredMode90, mDisplay->takeDesiredMode());
     EXPECT_FALSE(mDisplay->getDesiredMode());
 }
 
-TEST_F(InitiateModeChangeTest, initiateModeChange) REQUIRES(kMainThreadContext) {
+TEST_F(InitiateModeChangeTest, initiateModeChange) FTL_FAKE_GUARD(kMainThreadContext) {
     EXPECT_EQ(Action::InitiateDisplayModeSwitch,
               mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode90)));
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, mDisplay->getDesiredMode());
+    EXPECT_DISPLAY_MODE_REQUEST_OPT(kDesiredMode90, mDisplay->getDesiredMode());
 
     const hal::VsyncPeriodChangeConstraints constraints{
             .desiredTimeNanos = systemTime(),
             .seamlessRequired = false,
     };
     hal::VsyncPeriodChangeTimeline timeline;
-    EXPECT_TRUE(mDisplay->initiateModeChange(*mDisplay->getDesiredMode(), constraints, timeline));
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, mDisplay->getPendingMode());
 
-    mDisplay->clearDesiredMode();
+    auto desiredModeOpt = mDisplay->takeDesiredMode();
+    ASSERT_TRUE(desiredModeOpt);
     EXPECT_FALSE(mDisplay->getDesiredMode());
+
+    EXPECT_TRUE(mDisplay->initiateModeChange(std::move(*desiredModeOpt), constraints, timeline));
+
+    auto modeChange = mDisplay->finalizeModeChange();
+
+    auto* changePtr = std::get_if<DisplayDevice::RefreshRateChange>(&modeChange);
+    ASSERT_TRUE(changePtr);
+    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, changePtr->activeMode);
 }
 
 TEST_F(InitiateModeChangeTest, initiateRenderRateSwitch) {
@@ -125,27 +136,47 @@
 TEST_F(InitiateModeChangeTest, initiateDisplayModeSwitch) FTL_FAKE_GUARD(kMainThreadContext) {
     EXPECT_EQ(Action::InitiateDisplayModeSwitch,
               mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode90)));
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, mDisplay->getDesiredMode());
+    EXPECT_DISPLAY_MODE_REQUEST_OPT(kDesiredMode90, mDisplay->getDesiredMode());
 
     const hal::VsyncPeriodChangeConstraints constraints{
             .desiredTimeNanos = systemTime(),
             .seamlessRequired = false,
     };
     hal::VsyncPeriodChangeTimeline timeline;
-    EXPECT_TRUE(mDisplay->initiateModeChange(*mDisplay->getDesiredMode(), constraints, timeline));
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, mDisplay->getPendingMode());
 
-    EXPECT_EQ(Action::None, mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode120)));
-    ASSERT_TRUE(mDisplay->getDesiredMode());
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode120, mDisplay->getDesiredMode());
-
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, mDisplay->getPendingMode());
-
-    EXPECT_TRUE(mDisplay->initiateModeChange(*mDisplay->getDesiredMode(), constraints, timeline));
-    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode120, mDisplay->getPendingMode());
-
-    mDisplay->clearDesiredMode();
+    auto desiredModeOpt = mDisplay->takeDesiredMode();
+    ASSERT_TRUE(desiredModeOpt);
     EXPECT_FALSE(mDisplay->getDesiredMode());
+
+    EXPECT_TRUE(mDisplay->initiateModeChange(std::move(*desiredModeOpt), constraints, timeline));
+
+    auto modeChange = mDisplay->finalizeModeChange();
+    auto* changePtr = std::get_if<DisplayDevice::RefreshRateChange>(&modeChange);
+    ASSERT_TRUE(changePtr);
+    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode90, changePtr->activeMode);
+
+    // The latest request should override the desired mode.
+    EXPECT_EQ(Action::InitiateDisplayModeSwitch,
+              mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode60)));
+    EXPECT_EQ(Action::None, mDisplay->setDesiredMode(DisplayModeRequest(kDesiredMode120)));
+
+    EXPECT_DISPLAY_MODE_REQUEST_OPT(kDesiredMode120, mDisplay->getDesiredMode());
+
+    // No pending mode change.
+    EXPECT_TRUE(
+            std::holds_alternative<DisplayDevice::NoModeChange>(mDisplay->finalizeModeChange()));
+
+    desiredModeOpt = mDisplay->takeDesiredMode();
+    ASSERT_TRUE(desiredModeOpt);
+    EXPECT_FALSE(mDisplay->getDesiredMode());
+
+    EXPECT_TRUE(mDisplay->initiateModeChange(std::move(*desiredModeOpt), constraints, timeline));
+
+    modeChange = mDisplay->finalizeModeChange();
+
+    changePtr = std::get_if<DisplayDevice::RefreshRateChange>(&modeChange);
+    ASSERT_TRUE(changePtr);
+    EXPECT_DISPLAY_MODE_REQUEST(kDesiredMode120, changePtr->activeMode);
 }
 
 } // namespace
diff --git a/services/surfaceflinger/tests/unittests/SurfaceFlinger_DisplayModeSwitching.cpp b/services/surfaceflinger/tests/unittests/SurfaceFlinger_DisplayModeSwitching.cpp
index 7ad97a2..1af4a7a 100644
--- a/services/surfaceflinger/tests/unittests/SurfaceFlinger_DisplayModeSwitching.cpp
+++ b/services/surfaceflinger/tests/unittests/SurfaceFlinger_DisplayModeSwitching.cpp
@@ -179,7 +179,7 @@
 
     Mock::VerifyAndClearExpectations(mComposer);
 
-    EXPECT_TRUE(mDisplay->getDesiredMode());
+    EXPECT_FALSE(mDisplay->getDesiredMode());
     EXPECT_EQ(mDisplay->getActiveMode().modePtr->getId(), kModeId60);
 
     // Verify that the next commit will complete the mode change and send
@@ -263,11 +263,13 @@
 
     mFlinger.commit();
 
-    ASSERT_TRUE(mDisplay->getDesiredMode());
-    EXPECT_EQ(mDisplay->getDesiredMode()->mode.modePtr->getId(), kModeId120);
+    // The 120 Hz mode should be pending.
+    EXPECT_FALSE(mDisplay->getDesiredMode());
+    EXPECT_EQ(mDisplay->getActiveMode().modePtr->getId(), kModeId90);
 
     mFlinger.commit();
 
+    // The 120 Hz mode should be active.
     EXPECT_FALSE(mDisplay->getDesiredMode());
     EXPECT_EQ(mDisplay->getActiveMode().modePtr->getId(), kModeId120);
 }
@@ -324,7 +326,7 @@
     EXPECT_EQ(mDisplay->getActiveMode().modePtr->getId(), kModeId90_4K);
 }
 
-MATCHER_P2(ModeSwitchingTo, flinger, modeId, "") {
+MATCHER_P2(HasDesiredMode, flinger, modeId, "") {
     if (!arg->getDesiredMode()) {
         *result_listener << "No desired mode";
         return false;
@@ -343,12 +345,33 @@
     return true;
 }
 
-MATCHER_P(ModeSettledTo, modeId, "") {
+MATCHER_P(HasPendingMode, modeId, "") {
+    const auto pendingOpt = TestableSurfaceFlinger::getPendingMode(arg);
+
+    if (!pendingOpt) {
+        *result_listener << "No pending mode";
+        return false;
+    }
+
+    if (pendingOpt->mode.modePtr->getId() != modeId) {
+        *result_listener << "Unexpected pending mode " << modeId;
+        return false;
+    }
+
+    return true;
+}
+
+MATCHER_P(HasActiveMode, modeId, "") {
     if (const auto desiredOpt = arg->getDesiredMode()) {
         *result_listener << "Unsettled desired mode " << desiredOpt->mode.modePtr->getId();
         return false;
     }
 
+    if (const auto pendingOpt = TestableSurfaceFlinger::getPendingMode(arg)) {
+        *result_listener << "Unsettled pending mode " << pendingOpt->mode.modePtr->getId();
+        return false;
+    }
+
     ftl::FakeGuard guard(kMainThreadContext);
 
     if (arg->getActiveMode().modePtr->getId() != modeId) {
@@ -365,14 +388,14 @@
     EXPECT_TRUE(innerDisplay->isPoweredOn());
     EXPECT_FALSE(outerDisplay->isPoweredOn());
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId60));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId60));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     // Only the inner display is powered on.
     mFlinger.onActiveDisplayChanged(nullptr, *innerDisplay);
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId60));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId60));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     EXPECT_EQ(NO_ERROR,
               mFlinger.setDesiredDisplayModeSpecs(innerDisplay->getDisplayToken().promote(),
@@ -384,8 +407,8 @@
                                                   mock::createDisplayModeSpecs(kModeId60.value(),
                                                                                false, 0.f, 120.f)));
 
-    EXPECT_THAT(innerDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasDesiredMode(&mFlinger, kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     const VsyncPeriodChangeTimeline timeline{.refreshRequired = true};
     EXPECT_CALL(*mComposer,
@@ -395,13 +418,13 @@
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasPendingMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     innerDisplay->setPowerMode(hal::PowerMode::OFF);
     outerDisplay->setPowerMode(hal::PowerMode::ON);
@@ -409,8 +432,8 @@
     // Only the outer display is powered on.
     mFlinger.onActiveDisplayChanged(innerDisplay.get(), *outerDisplay);
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSwitchingTo(&mFlinger, kModeId60));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasDesiredMode(&mFlinger, kModeId60));
 
     EXPECT_CALL(*mComposer,
                 setActiveConfigWithConstraints(kOuterDisplayHwcId,
@@ -419,13 +442,13 @@
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSwitchingTo(&mFlinger, kModeId60));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasPendingMode(kModeId60));
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId60));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId60));
 }
 
 TEST_F(DisplayModeSwitchingTest, innerAndOuterDisplay) {
@@ -434,16 +457,16 @@
     EXPECT_TRUE(innerDisplay->isPoweredOn());
     EXPECT_FALSE(outerDisplay->isPoweredOn());
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId60));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId60));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     outerDisplay->setPowerMode(hal::PowerMode::ON);
 
     // Both displays are powered on.
     mFlinger.onActiveDisplayChanged(nullptr, *innerDisplay);
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId60));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId60));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     EXPECT_EQ(NO_ERROR,
               mFlinger.setDesiredDisplayModeSpecs(innerDisplay->getDisplayToken().promote(),
@@ -455,8 +478,8 @@
                                                   mock::createDisplayModeSpecs(kModeId60.value(),
                                                                                false, 0.f, 120.f)));
 
-    EXPECT_THAT(innerDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSwitchingTo(&mFlinger, kModeId60));
+    EXPECT_THAT(innerDisplay, HasDesiredMode(&mFlinger, kModeId90));
+    EXPECT_THAT(outerDisplay, HasDesiredMode(&mFlinger, kModeId60));
 
     const VsyncPeriodChangeTimeline timeline{.refreshRequired = true};
     EXPECT_CALL(*mComposer,
@@ -471,25 +494,25 @@
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSwitchingTo(&mFlinger, kModeId60));
+    EXPECT_THAT(innerDisplay, HasPendingMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasPendingMode(kModeId60));
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId60));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId60));
 }
 
 TEST_F(DisplayModeSwitchingTest, powerOffDuringModeSet) {
     EXPECT_TRUE(mDisplay->isPoweredOn());
-    EXPECT_THAT(mDisplay, ModeSettledTo(kModeId60));
+    EXPECT_THAT(mDisplay, HasActiveMode(kModeId60));
 
     EXPECT_EQ(NO_ERROR,
               mFlinger.setDesiredDisplayModeSpecs(mDisplay->getDisplayToken().promote(),
                                                   mock::createDisplayModeSpecs(kModeId90.value(),
                                                                                false, 0.f, 120.f)));
 
-    EXPECT_THAT(mDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
+    EXPECT_THAT(mDisplay, HasDesiredMode(&mFlinger, kModeId90));
 
     // Power off the display before the mode has been set.
     mDisplay->setPowerMode(hal::PowerMode::OFF);
@@ -504,11 +527,11 @@
 
     // Powering off should not abort the mode set.
     EXPECT_FALSE(mDisplay->isPoweredOn());
-    EXPECT_THAT(mDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
+    EXPECT_THAT(mDisplay, HasPendingMode(kModeId90));
 
     mFlinger.commit();
 
-    EXPECT_THAT(mDisplay, ModeSettledTo(kModeId90));
+    EXPECT_THAT(mDisplay, HasActiveMode(kModeId90));
 }
 
 TEST_F(DisplayModeSwitchingTest, powerOffDuringConcurrentModeSet) {
@@ -517,16 +540,16 @@
     EXPECT_TRUE(innerDisplay->isPoweredOn());
     EXPECT_FALSE(outerDisplay->isPoweredOn());
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId60));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId60));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     outerDisplay->setPowerMode(hal::PowerMode::ON);
 
     // Both displays are powered on.
     mFlinger.onActiveDisplayChanged(nullptr, *innerDisplay);
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId60));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId60));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     EXPECT_EQ(NO_ERROR,
               mFlinger.setDesiredDisplayModeSpecs(innerDisplay->getDisplayToken().promote(),
@@ -538,8 +561,8 @@
                                                   mock::createDisplayModeSpecs(kModeId60.value(),
                                                                                false, 0.f, 120.f)));
 
-    EXPECT_THAT(innerDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSwitchingTo(&mFlinger, kModeId60));
+    EXPECT_THAT(innerDisplay, HasDesiredMode(&mFlinger, kModeId90));
+    EXPECT_THAT(outerDisplay, HasDesiredMode(&mFlinger, kModeId60));
 
     // Power off the outer display before the mode has been set.
     outerDisplay->setPowerMode(hal::PowerMode::OFF);
@@ -553,13 +576,13 @@
     mFlinger.commit();
 
     // Powering off the inactive display should abort the mode set.
-    EXPECT_THAT(innerDisplay, ModeSwitchingTo(&mFlinger, kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasPendingMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId120));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId120));
 
     innerDisplay->setPowerMode(hal::PowerMode::OFF);
     outerDisplay->setPowerMode(hal::PowerMode::ON);
@@ -575,13 +598,13 @@
     mFlinger.commit();
 
     // The mode set should resume once the display becomes active.
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSwitchingTo(&mFlinger, kModeId60));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasPendingMode(kModeId60));
 
     mFlinger.commit();
 
-    EXPECT_THAT(innerDisplay, ModeSettledTo(kModeId90));
-    EXPECT_THAT(outerDisplay, ModeSettledTo(kModeId60));
+    EXPECT_THAT(innerDisplay, HasActiveMode(kModeId90));
+    EXPECT_THAT(outerDisplay, HasActiveMode(kModeId60));
 }
 
 } // namespace
diff --git a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
index 22cb24b..47d64d3 100644
--- a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
+++ b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
@@ -484,6 +484,10 @@
         return mFlinger->setDisplayBrightness(display, brightness);
     }
 
+    static const auto& getPendingMode(const sp<DisplayDevice>& display) {
+        return display->mPendingModeOpt;
+    }
+
     // Allow reading display state without locking, as if called on the SF main thread.
     auto setPowerModeInternal(const sp<DisplayDevice>& display,
                               hal::PowerMode mode) NO_THREAD_SAFETY_ANALYSIS {