SF: omit vsync callbacks when screen is OFF

This CL is submitted behind a flag and in still in development.
The flag should not be enabled just yet.

Test: manual
Bug: 331636736
Flag: com.android.graphics.surfaceflinger.flags.no_vsyncs_on_screen_off
Change-Id: Iec9cde3bafb9c112c9ce9beebe6dded4727fc99c

Author: adyabr

services/surfaceflinger/DisplayDevice.cpp

@@ -201,6 +201,10 @@ bool DisplayDevice::isPoweredOn() const {
     return mPowerMode != hal::PowerMode::OFF;
 }
 
+bool DisplayDevice::isRefreshable() const {
+    return mPowerMode == hal::PowerMode::DOZE || mPowerMode == hal::PowerMode::ON;
+}
+
 ui::Dataspace DisplayDevice::getCompositionDataSpace() const {
     return mCompositionDisplay->getState().dataspace;
 }

services/surfaceflinger/DisplayDevice.h

@@ -173,6 +173,7 @@ class DisplayDevice : public RefBase {
     hardware::graphics::composer::hal::PowerMode getPowerMode() const;
     void setPowerMode(hardware::graphics::composer::hal::PowerMode);
     bool isPoweredOn() const;
+    bool isRefreshable() const;
     void tracePowerMode();
 
     // Enables layer caching on this DisplayDevice

services/surfaceflinger/Scheduler/EventThread.cpp

@@ -420,6 +420,16 @@ void EventThread::enableSyntheticVsync(bool enable) {
     mCondition.notify_all();
 }
 
+void EventThread::omitVsyncDispatching(bool omitted) {
+    std::lock_guard<std::mutex> lock(mMutex);
+    if (!mVSyncState || mVSyncState->omitted == omitted) {
+        return;
+    }
+
+    mVSyncState->omitted = omitted;
+    mCondition.notify_all();
+}
+
 void EventThread::onVsync(nsecs_t vsyncTime, nsecs_t wakeupTime, nsecs_t readyTime) {
     std::lock_guard<std::mutex> lock(mMutex);
     mLastVsyncCallbackTime = TimePoint::fromNs(vsyncTime);
@@ -521,7 +531,17 @@ void EventThread::threadMain(std::unique_lock<std::mutex>& lock) {
         }
 
         if (mVSyncState && vsyncRequested) {
-            mState = mVSyncState->synthetic ? State::SyntheticVSync : State::VSync;
+            const bool vsyncOmitted =
+                    FlagManager::getInstance().no_vsyncs_on_screen_off() && mVSyncState->omitted;
+            if (vsyncOmitted) {
+                mState = State::Idle;
+                SFTRACE_INT("VsyncPendingScreenOn", 1);
+            } else {
+                mState = mVSyncState->synthetic ? State::SyntheticVSync : State::VSync;
+                if (FlagManager::getInstance().no_vsyncs_on_screen_off()) {
+                    SFTRACE_INT("VsyncPendingScreenOn", 0);
+                }
+            }
         } else {
             ALOGW_IF(!mVSyncState, "Ignoring VSYNC request while display is disconnected");
             mState = State::Idle;

services/surfaceflinger/Scheduler/EventThread.h

@@ -106,6 +106,8 @@ class EventThread {
     // Feed clients with fake VSYNC, e.g. while the display is off.
     virtual void enableSyntheticVsync(bool) = 0;
 
+    virtual void omitVsyncDispatching(bool) = 0;
+
     virtual void onHotplugReceived(PhysicalDisplayId displayId, bool connected) = 0;
 
     virtual void onHotplugConnectionError(int32_t connectionError) = 0;
@@ -165,6 +167,8 @@ class EventThread : public android::EventThread {
 
     void enableSyntheticVsync(bool) override;
 
+    void omitVsyncDispatching(bool) override;
+
     void onHotplugReceived(PhysicalDisplayId displayId, bool connected) override;
 
     void onHotplugConnectionError(int32_t connectionError) override;
@@ -240,6 +244,9 @@ class EventThread : public android::EventThread {
 
         // True if VSYNC should be faked, e.g. when display is off.
         bool synthetic = false;
+
+        // True if VSYNC should not be delivered to apps. Used when the display is off.
+        bool omitted = false;
     };
 
     // TODO(b/74619554): Create per-display threads waiting on respective VSYNC signals,

services/surfaceflinger/Scheduler/Scheduler.cpp

@@ -405,6 +405,14 @@ void Scheduler::enableSyntheticVsync(bool enable) {
     eventThreadFor(Cycle::Render).enableSyntheticVsync(enable);
 }
 
+void Scheduler::omitVsyncDispatching(bool omitted) {
+    eventThreadFor(Cycle::Render).omitVsyncDispatching(omitted);
+    // Note: If we don't couple Cycle::LastComposite event thread, there is a black screen
+    // after boot. This is most likely sysui or system_server dependency on sf instance
+    // Choreographer
+    eventThreadFor(Cycle::LastComposite).omitVsyncDispatching(omitted);
+}
+
 void Scheduler::onFrameRateOverridesChanged() {
     const auto [pacesetterId, supportsFrameRateOverrideByContent] = [this] {
         std::scoped_lock lock(mDisplayLock);

services/surfaceflinger/Scheduler/Scheduler.h

@@ -154,6 +154,7 @@ class Scheduler : public IEventThreadCallback, android::impl::MessageQueue {
     bool onDisplayModeChanged(PhysicalDisplayId, const FrameRateMode&) EXCLUDES(mPolicyLock);
 
     void enableSyntheticVsync(bool = true) REQUIRES(kMainThreadContext);
+    void omitVsyncDispatching(bool) REQUIRES(kMainThreadContext);
 
     void onHdcpLevelsChanged(Cycle, PhysicalDisplayId, int32_t, int32_t);
 

services/surfaceflinger/SurfaceFlinger.cpp

@@ -3660,6 +3660,26 @@ sp<DisplayDevice> SurfaceFlinger::setupNewDisplayDeviceInternal(
     return display;
 }
 
+void SurfaceFlinger::incRefreshableDisplays() {
+    if (FlagManager::getInstance().no_vsyncs_on_screen_off()) {
+        mRefreshableDisplays++;
+        if (mRefreshableDisplays == 1) {
+            ftl::FakeGuard guard(kMainThreadContext);
+            mScheduler->omitVsyncDispatching(false);
+        }
+    }
+}
+
+void SurfaceFlinger::decRefreshableDisplays() {
+    if (FlagManager::getInstance().no_vsyncs_on_screen_off()) {
+        mRefreshableDisplays--;
+        if (mRefreshableDisplays == 0) {
+            ftl::FakeGuard guard(kMainThreadContext);
+            mScheduler->omitVsyncDispatching(true);
+        }
+    }
+}
+
 void SurfaceFlinger::processDisplayAdded(const wp<IBinder>& displayToken,
                                          const DisplayDeviceState& state) {
     ui::Size resolution(0, 0);
@@ -3751,6 +3771,10 @@ void SurfaceFlinger::processDisplayAdded(const wp<IBinder>& displayToken,
         display->adjustRefreshRate(mScheduler->getPacesetterRefreshRate());
     }
 
+    if (display->isRefreshable()) {
+        incRefreshableDisplays();
+    }
+
     mDisplays.try_emplace(displayToken, std::move(display));
 
     // For an external display, loadDisplayModes already attempted to select the same mode
@@ -3785,6 +3809,10 @@ void SurfaceFlinger::processDisplayRemoved(const wp<IBinder>& displayToken) {
         } else {
             mScheduler->unregisterDisplay(display->getPhysicalId(), mActiveDisplayId);
         }
+
+        if (display->isRefreshable()) {
+            decRefreshableDisplays();
+        }
     }
 
     mDisplays.erase(displayToken);
@@ -3819,6 +3847,10 @@ void SurfaceFlinger::processDisplayChanged(const wp<IBinder>& displayToken,
             if (display->isVirtual()) {
                 releaseVirtualDisplay(display->getVirtualId());
             }
+
+            if (display->isRefreshable()) {
+                decRefreshableDisplays();
+            }
         }
 
         mDisplays.erase(displayToken);
@@ -5317,7 +5349,15 @@ void SurfaceFlinger::setPowerModeInternal(const sp<DisplayDevice>& display, hal:
                      activeDisplay->isPoweredOn(),
              "Trying to change power mode on inactive display without powering off active display");
 
+    const bool couldRefresh = display->isRefreshable();
     display->setPowerMode(mode);
+    const bool canRefresh = display->isRefreshable();
+
+    if (couldRefresh && !canRefresh) {
+        decRefreshableDisplays();
+    } else if (!couldRefresh && canRefresh) {
+        incRefreshableDisplays();
+    }
 
     const auto activeMode = display->refreshRateSelector().getActiveMode().modePtr;
     if (currentMode == hal::PowerMode::OFF) {

services/surfaceflinger/SurfaceFlinger.h

@@ -1423,6 +1423,11 @@ class SurfaceFlinger : public BnSurfaceComposer,
     // Whether a display should be turned on when initialized
     bool mSkipPowerOnForQuiescent;
 
+    // used for omitting vsync callbacks to apps when the display is not updatable
+    int mRefreshableDisplays GUARDED_BY(mStateLock) = 0;
+    void incRefreshableDisplays() REQUIRES(mStateLock);
+    void decRefreshableDisplays() REQUIRES(mStateLock);
+
     frontend::LayerLifecycleManager mLayerLifecycleManager GUARDED_BY(kMainThreadContext);
     frontend::LayerHierarchyBuilder mLayerHierarchyBuilder GUARDED_BY(kMainThreadContext);
     frontend::LayerSnapshotBuilder mLayerSnapshotBuilder GUARDED_BY(kMainThreadContext);

services/surfaceflinger/tests/unittests/mock/MockEventThread.h

@@ -30,6 +30,7 @@ class EventThread : public android::EventThread {
     MOCK_METHOD(sp<EventThreadConnection>, createEventConnection, (EventRegistrationFlags),
                 (const, override));
     MOCK_METHOD(void, enableSyntheticVsync, (bool), (override));
+    MOCK_METHOD(void, omitVsyncDispatching, (bool), (override));
     MOCK_METHOD(void, onHotplugReceived, (PhysicalDisplayId, bool), (override));
     MOCK_METHOD(void, onHotplugConnectionError, (int32_t), (override));
     MOCK_METHOD(void, onModeChanged, (const scheduler::FrameRateMode&), (override));