Improve teardown of DrmGpu

src/plugins/platforms/drm/drm_backend.cpp

@@ -73,13 +73,7 @@ DrmBackend::DrmBackend(QObject *parent)
 
 DrmBackend::~DrmBackend()
 {
-    if (m_gpus.size() > 0) {
-        // wait for pageflips
-        while (m_pageFlipsPending != 0) {
-            QCoreApplication::processEvents(QEventLoop::WaitForMoreEvents);
-        }
-        qDeleteAll(m_gpus);
-    }
+    qDeleteAll(m_gpus);
 }
 
 void DrmBackend::init()
@@ -185,8 +179,6 @@ void DrmBackend::reactivate()
             o->moveCursor();
         }
     }
-    // restart compositor
-    m_pageFlipsPending = 0;
 
     for (DrmOutput *output : qAsConst(m_outputs)) {
         output->renderLoop()->uninhibit();
@@ -238,9 +230,7 @@ void DrmBackend::pageFlipHandler(int fd, unsigned int frame, unsigned int sec, u
     Q_UNUSED(frame)
 
     auto output = static_cast<DrmOutput *>(data);
-
     DrmGpu *gpu = output->gpu();
-    DrmBackend *backend = output->m_backend;
 
     std::chrono::nanoseconds timestamp = convertTimestamp(gpu->presentationClock(),
                                                           CLOCK_MONOTONIC,
@@ -252,8 +242,6 @@ void DrmBackend::pageFlipHandler(int fd, unsigned int frame, unsigned int sec, u
     }
 
     output->pageFlipped();
-    backend->m_pageFlipsPending--;
-
     RenderLoopPrivate *renderLoopPrivate = RenderLoopPrivate::get(output->renderLoop());
     renderLoopPrivate->notifyFrameCompleted(timestamp);
 }
@@ -538,7 +526,6 @@ bool DrmBackend::present(DrmBuffer *buffer, DrmOutput *output)
     }
 
     if (output->present(buffer)) {
-        m_pageFlipsPending++;
         return true;
     } else if (output->gpu()->deleteBufferAfterPageFlip()) {
         delete buffer;

src/plugins/platforms/drm/drm_backend.h

@@ -115,7 +115,6 @@ private:
     // active and enabled pipelines (above + wl_output)
     QVector<DrmOutput*> m_enabledOutputs;
 
-    int m_pageFlipsPending = 0;
     bool m_active = false;
     QVector<DrmGpu*> m_gpus;
     QScopedPointer<DpmsInputEventFilter> m_dpmsFilter;

src/plugins/platforms/drm/drm_gpu.cpp

@@ -68,6 +68,7 @@ DrmGpu::DrmGpu(DrmBackend *backend, QByteArray devNode, int fd, int drmId) : m_b
 
 DrmGpu::~DrmGpu()
 {
+    waitIdle();
     if (m_eglDisplay != EGL_NO_DISPLAY) {
         eglTerminate(m_eglDisplay);
     }
@@ -325,4 +326,34 @@ void DrmGpu::dispatchEvents()
     drmHandleEvent(m_fd, &context);
 }
 
+void DrmGpu::waitIdle()
+{
+    m_socketNotifier->setEnabled(false);
+    while (true) {
+        const bool idle = std::all_of(m_outputs.constBegin(), m_outputs.constEnd(), [](DrmOutput *output){
+            return !output->m_pageFlipPending;
+        });
+        if (idle) {
+            break;
+        }
+        fd_set set;
+        FD_ZERO(&set);
+        FD_SET(m_fd, &set);
+        timeval timeout;
+        timeout.tv_sec = 30;
+        timeout.tv_usec = 0;
+        const int descriptorCount = select(m_fd + 1, &set, nullptr, nullptr, &timeout);
+        if (descriptorCount < 0) {
+            qCWarning(KWIN_DRM) << "select() in DrmGpu::waitIdle failed:" << strerror(errno);
+            break;
+        } else if (FD_ISSET(m_fd, &set)) {
+            dispatchEvents();
+        } else {
+            qCWarning(KWIN_DRM) << "No drm events for gpu" << m_devNode << "within last 30 seconds";
+            break;
+        }
+    };
+    m_socketNotifier->setEnabled(true);
+}
+
 }

src/plugins/platforms/drm/drm_gpu.h

@@ -104,6 +104,8 @@ public:
      */
     clockid_t presentationClock() const;
 
+    void waitIdle();
+
 Q_SIGNALS:
     void outputAdded(DrmOutput *output);
     void outputRemoved(DrmOutput *output);

src/plugins/platforms/drm/drm_output.cpp

@@ -834,6 +834,7 @@ bool DrmOutput::presentLegacy(DrmBuffer *buffer)
     const bool ok = drmModePageFlip(m_gpu->fd(), m_crtc->id(), buffer->bufferId(), DRM_MODE_PAGE_FLIP_EVENT, this) == 0;
     if (ok) {
         m_crtc->setNext(buffer);
+        m_pageFlipPending = true;
     } else {
         qCWarning(KWIN_DRM) << "Page flip failed:" << strerror(errno);
     }