diff --git a/services/inputflinger/reader/Android.bp b/services/inputflinger/reader/Android.bp
index e76b648..b2f15b4 100644
--- a/services/inputflinger/reader/Android.bp
+++ b/services/inputflinger/reader/Android.bp
@@ -78,6 +78,7 @@
     name: "libinputreader_defaults",
     srcs: [":libinputreader_sources"],
     shared_libs: [
+        "android.companion.virtualdevice.flags-aconfig-cc-host",
         "libbase",
         "libcap",
         "libcrypto",
diff --git a/services/inputflinger/reader/EventHub.cpp b/services/inputflinger/reader/EventHub.cpp
index fe70a51..540f55d 100644
--- a/services/inputflinger/reader/EventHub.cpp
+++ b/services/inputflinger/reader/EventHub.cpp
@@ -33,6 +33,8 @@
 #include <sys/sysmacros.h>
 #include <unistd.h>
 
+#include <android_companion_virtualdevice_flags.h>
+
 #define LOG_TAG "EventHub"
 
 // #define LOG_NDEBUG 0
@@ -68,6 +70,8 @@
 
 namespace android {
 
+namespace vd_flags = android::companion::virtualdevice::flags;
+
 using namespace ftl::flag_operators;
 
 static const char* DEVICE_INPUT_PATH = "/dev/input";
@@ -2503,6 +2507,12 @@
         }
     }
 
+    // See if the device is a rotary encoder with a single scroll axis and nothing else.
+    if (vd_flags::virtual_rotary() && device->classes == ftl::Flags<InputDeviceClass>(0) &&
+        device->relBitmask.test(REL_WHEEL) && !device->relBitmask.test(REL_HWHEEL)) {
+        device->classes |= InputDeviceClass::ROTARY_ENCODER;
+    }
+
     // If the device isn't recognized as something we handle, don't monitor it.
     if (device->classes == ftl::Flags<InputDeviceClass>(0)) {
         ALOGV("Dropping device: id=%d, path='%s', name='%s'", deviceId, devicePath.c_str(),
diff --git a/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.cpp b/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.cpp
index 27ff52f..20fd359 100644
--- a/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.cpp
+++ b/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.cpp
@@ -84,12 +84,18 @@
         }
     }
     if (!changes.any() || changes.test(InputReaderConfiguration::Change::DISPLAY_INFO)) {
-        std::optional<DisplayViewport> internalViewport =
-                config.getDisplayViewportByType(ViewportType::INTERNAL);
-        if (internalViewport) {
-            mOrientation = internalViewport->orientation;
+        if (getDeviceContext().getAssociatedViewport()) {
+            mDisplayId = getDeviceContext().getAssociatedViewport()->displayId;
+            mOrientation = getDeviceContext().getAssociatedViewport()->orientation;
         } else {
-            mOrientation = ui::ROTATION_0;
+            mDisplayId = ui::LogicalDisplayId::INVALID;
+            std::optional<DisplayViewport> internalViewport =
+                    config.getDisplayViewportByType(ViewportType::INTERNAL);
+            if (internalViewport) {
+                mOrientation = internalViewport->orientation;
+            } else {
+                mOrientation = ui::ROTATION_0;
+            }
         }
     }
     return out;
@@ -124,8 +130,6 @@
     // Send motion event.
     if (scrolled) {
         int32_t metaState = getContext()->getGlobalMetaState();
-        // This is not a pointer, so it's not associated with a display.
-        ui::LogicalDisplayId displayId = ui::LogicalDisplayId::INVALID;
 
         if (mOrientation == ui::ROTATION_180) {
             scroll = -scroll;
@@ -147,7 +151,7 @@
 
         out.push_back(
                 NotifyMotionArgs(getContext()->getNextId(), when, readTime, getDeviceId(), mSource,
-                                 displayId, policyFlags, AMOTION_EVENT_ACTION_SCROLL, 0, 0,
+                                 mDisplayId, policyFlags, AMOTION_EVENT_ACTION_SCROLL, 0, 0,
                                  metaState, /*buttonState=*/0, MotionClassification::NONE,
                                  AMOTION_EVENT_EDGE_FLAG_NONE, 1, &pointerProperties,
                                  &pointerCoords, 0, 0, AMOTION_EVENT_INVALID_CURSOR_POSITION,
diff --git a/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.h b/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.h
index 14c540b..7e80415 100644
--- a/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.h
+++ b/services/inputflinger/reader/mapper/RotaryEncoderInputMapper.h
@@ -47,6 +47,7 @@
     int32_t mSource;
     float mScalingFactor;
     ui::Rotation mOrientation;
+    ui::LogicalDisplayId mDisplayId = ui::LogicalDisplayId::INVALID;
     std::unique_ptr<SlopController> mSlopController;
 
     explicit RotaryEncoderInputMapper(InputDeviceContext& deviceContext,
diff --git a/services/inputflinger/tests/Android.bp b/services/inputflinger/tests/Android.bp
index cf0d46a..bddf43e 100644
--- a/services/inputflinger/tests/Android.bp
+++ b/services/inputflinger/tests/Android.bp
@@ -76,6 +76,7 @@
         "PointerChoreographer_test.cpp",
         "PreferStylusOverTouch_test.cpp",
         "PropertyProvider_test.cpp",
+        "RotaryEncoderInputMapper_test.cpp",
         "SlopController_test.cpp",
         "SyncQueue_test.cpp",
         "TimerProvider_test.cpp",
diff --git a/services/inputflinger/tests/RotaryEncoderInputMapper_test.cpp b/services/inputflinger/tests/RotaryEncoderInputMapper_test.cpp
new file mode 100644
index 0000000..94cfc32
--- /dev/null
+++ b/services/inputflinger/tests/RotaryEncoderInputMapper_test.cpp
@@ -0,0 +1,169 @@
+/*
+ * 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.
+ */
+
+#include "RotaryEncoderInputMapper.h"
+
+#include <list>
+#include <string>
+#include <tuple>
+#include <variant>
+
+#include <android-base/logging.h>
+#include <gtest/gtest.h>
+#include <input/DisplayViewport.h>
+#include <linux/input-event-codes.h>
+#include <linux/input.h>
+#include <utils/Timers.h>
+
+#include "InputMapperTest.h"
+#include "InputReaderBase.h"
+#include "InterfaceMocks.h"
+#include "NotifyArgs.h"
+#include "TestEventMatchers.h"
+#include "ui/Rotation.h"
+
+#define TAG "RotaryEncoderInputMapper_test"
+
+namespace android {
+
+using testing::AllOf;
+using testing::Return;
+using testing::VariantWith;
+constexpr ui::LogicalDisplayId DISPLAY_ID = ui::LogicalDisplayId::DEFAULT;
+constexpr ui::LogicalDisplayId SECONDARY_DISPLAY_ID = ui::LogicalDisplayId{DISPLAY_ID.val() + 1};
+constexpr int32_t DISPLAY_WIDTH = 480;
+constexpr int32_t DISPLAY_HEIGHT = 800;
+
+namespace {
+
+DisplayViewport createViewport() {
+    DisplayViewport v;
+    v.orientation = ui::Rotation::Rotation0;
+    v.logicalRight = DISPLAY_HEIGHT;
+    v.logicalBottom = DISPLAY_WIDTH;
+    v.physicalRight = DISPLAY_HEIGHT;
+    v.physicalBottom = DISPLAY_WIDTH;
+    v.deviceWidth = DISPLAY_HEIGHT;
+    v.deviceHeight = DISPLAY_WIDTH;
+    v.isActive = true;
+    return v;
+}
+
+DisplayViewport createPrimaryViewport() {
+    DisplayViewport v = createViewport();
+    v.displayId = DISPLAY_ID;
+    v.uniqueId = "local:1";
+    return v;
+}
+
+DisplayViewport createSecondaryViewport() {
+    DisplayViewport v = createViewport();
+    v.displayId = SECONDARY_DISPLAY_ID;
+    v.uniqueId = "local:2";
+    v.type = ViewportType::EXTERNAL;
+    return v;
+}
+
+/**
+ * A fake InputDeviceContext that allows the associated viewport to be specified for the mapper.
+ *
+ * This is currently necessary because InputMapperUnitTest doesn't register the mappers it creates
+ * with the InputDevice object, meaning that InputDevice::isIgnored becomes true, and the input
+ * device doesn't set its associated viewport when it's configured.
+ *
+ * TODO(b/319217713): work out a way to avoid this fake.
+ */
+class ViewportFakingInputDeviceContext : public InputDeviceContext {
+public:
+    ViewportFakingInputDeviceContext(InputDevice& device, int32_t eventHubId,
+                                     std::optional<DisplayViewport> viewport)
+          : InputDeviceContext(device, eventHubId), mAssociatedViewport(viewport) {}
+
+    ViewportFakingInputDeviceContext(InputDevice& device, int32_t eventHubId)
+          : ViewportFakingInputDeviceContext(device, eventHubId, createPrimaryViewport()) {}
+
+    std::optional<DisplayViewport> getAssociatedViewport() const override {
+        return mAssociatedViewport;
+    }
+
+    void setViewport(const std::optional<DisplayViewport>& viewport) {
+        mAssociatedViewport = viewport;
+    }
+
+private:
+    std::optional<DisplayViewport> mAssociatedViewport;
+};
+
+} // namespace
+
+/**
+ * Unit tests for RotaryEncoderInputMapper.
+ */
+class RotaryEncoderInputMapperTest : public InputMapperUnitTest {
+protected:
+    void SetUp() override { SetUpWithBus(BUS_USB); }
+    void SetUpWithBus(int bus) override {
+        InputMapperUnitTest::SetUpWithBus(bus);
+
+        EXPECT_CALL(mMockEventHub, hasRelativeAxis(EVENTHUB_ID, REL_WHEEL))
+                .WillRepeatedly(Return(true));
+        EXPECT_CALL(mMockEventHub, hasRelativeAxis(EVENTHUB_ID, REL_HWHEEL))
+                .WillRepeatedly(Return(false));
+    }
+};
+
+TEST_F(RotaryEncoderInputMapperTest, ConfigureDisplayIdWithAssociatedViewport) {
+    DisplayViewport primaryViewport = createPrimaryViewport();
+    DisplayViewport secondaryViewport = createSecondaryViewport();
+    mReaderConfiguration.setDisplayViewports({primaryViewport, secondaryViewport});
+
+    // Set up the secondary display as the associated viewport of the mapper.
+    createDevice();
+    ViewportFakingInputDeviceContext deviceContext(*mDevice, EVENTHUB_ID, secondaryViewport);
+    mMapper = createInputMapper<RotaryEncoderInputMapper>(deviceContext, mReaderConfiguration);
+
+    std::list<NotifyArgs> args;
+    // Ensure input events are generated for the secondary display.
+    args += process(ARBITRARY_TIME, EV_REL, REL_WHEEL, 1);
+    args += process(ARBITRARY_TIME, EV_SYN, SYN_REPORT, 0);
+    EXPECT_THAT(args,
+                ElementsAre(VariantWith<NotifyMotionArgs>(
+                        AllOf(WithMotionAction(AMOTION_EVENT_ACTION_SCROLL),
+                              WithSource(AINPUT_SOURCE_ROTARY_ENCODER),
+                              WithDisplayId(SECONDARY_DISPLAY_ID)))));
+}
+
+TEST_F(RotaryEncoderInputMapperTest, ConfigureDisplayIdNoAssociatedViewport) {
+    // Set up the default display.
+    mFakePolicy->clearViewports();
+    mFakePolicy->addDisplayViewport(createPrimaryViewport());
+
+    // Set up the mapper with no associated viewport.
+    createDevice();
+    mMapper = createInputMapper<RotaryEncoderInputMapper>(*mDeviceContext, mReaderConfiguration);
+
+    // Ensure input events are generated without display ID
+    std::list<NotifyArgs> args;
+    args += process(ARBITRARY_TIME, EV_REL, REL_WHEEL, 1);
+    args += process(ARBITRARY_TIME, EV_SYN, SYN_REPORT, 0);
+    EXPECT_THAT(args,
+                ElementsAre(VariantWith<NotifyMotionArgs>(
+                        AllOf(WithMotionAction(AMOTION_EVENT_ACTION_SCROLL),
+                              WithSource(AINPUT_SOURCE_ROTARY_ENCODER),
+                              WithDisplayId(ui::LogicalDisplayId::INVALID)))));
+}
+
+} // namespace android
\ No newline at end of file