backensd/drm: directly try presentation with changed properties

This optimizes out an unnecessary atomic test - instead of testing the new state and
then attempting to present with that new state, this just directly tries to present the
full state. If that commit fails, the backend just tries again with the safer presentation
mode.

src/backends/drm/drm_output.cpp

@@ -274,27 +274,27 @@ bool DrmOutput::present(const std::shared_ptr<OutputFrame> &frame)
     if (frame->contentType()) {
         type = DrmConnector::kwinToDrmContentType(*frame->contentType());
     }
-    if (m_pipeline->presentationMode() != frame->presentationMode() || type != m_pipeline->contentType()) {
-        m_pipeline->setPresentationMode(frame->presentationMode());
-        m_pipeline->setContentType(type);
-        if (DrmPipeline::commitPipelines({m_pipeline}, DrmPipeline::CommitMode::Test) == DrmPipeline::Error::None) {
-            m_pipeline->applyPendingChanges();
-        } else {
-            m_pipeline->revertPendingChanges();
-        }
-        m_renderLoop->setPresentationMode(m_pipeline->presentationMode());
-    }
     const bool needsModeset = gpu()->needsModeset();
     bool success;
     if (needsModeset) {
+        m_pipeline->setPresentationMode(PresentationMode::VSync);
+        m_pipeline->setContentType(DrmConnector::DrmContentType::Graphics);
         success = m_pipeline->maybeModeset();
     } else {
+        m_pipeline->setPresentationMode(frame->presentationMode());
+        m_pipeline->setContentType(type);
         DrmPipeline::Error err = m_pipeline->present();
+        if (err != DrmPipeline::Error::None && frame->presentationMode() != PresentationMode::VSync) {
+            // retry with a more basic presentation mode
+            m_pipeline->setPresentationMode(PresentationMode::VSync);
+            err = m_pipeline->present();
+        }
         success = err == DrmPipeline::Error::None;
         if (err == DrmPipeline::Error::InvalidArguments) {
             QTimer::singleShot(0, m_gpu->platform(), &DrmBackend::updateOutputs);
         }
     }
+    m_renderLoop->setPresentationMode(m_pipeline->presentationMode());
     if (success) {
         Q_EMIT outputChange(m_pipeline->primaryLayer()->currentDamage());
         return true;

src/backends/drm/drm_pipeline_legacy.cpp

@@ -26,11 +26,8 @@ namespace KWin
 
 DrmPipeline::Error DrmPipeline::presentLegacy()
 {
-    if (!m_pending.crtc->current()) {
-        Error err = legacyModeset();
-        if (err != Error::None) {
-            return err;
-        }
+    if (Error err = applyPendingChangesLegacy(); err != Error::None) {
+        return err;
     }
     const auto buffer = m_primaryLayer->currentBuffer();
     auto commit = std::make_unique<DrmLegacyCommit>(this, buffer);