From 3cafc2098147b7f6f656ba0b4cec5932cddfeed5 Mon Sep 17 00:00:00 2001
From: Xaver Hugl <xaver.hugl@gmail.com>
Date: Sat, 16 Dec 2023 22:03:20 +0100
Subject: [PATCH] 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          | 20 ++++++++++----------
 src/backends/drm/drm_pipeline_legacy.cpp |  7 ++-----
 2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/src/backends/drm/drm_output.cpp b/src/backends/drm/drm_output.cpp
index b54c2b07df..363cbf755a 100644
--- a/src/backends/drm/drm_output.cpp
+++ b/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;
diff --git a/src/backends/drm/drm_pipeline_legacy.cpp b/src/backends/drm/drm_pipeline_legacy.cpp
index cb471645eb..615e6804ed 100644
--- a/src/backends/drm/drm_pipeline_legacy.cpp
+++ b/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);