[platforms/drm] Restore previous mode if an atomic test fails

Summary:
When KWin successfully presents a new mode, it stores the current state
as the last working mode. If a new modeset is requested and the atomic
test fails, all is undone and reverted to this last knowing mode.

Currently included are:
 * the mode
 * global position
 * transformation

This is only done on a modeset not when going to DPMS.

Test Plan:
Selected the not working vertical rotation and nothing bad
happened.

Reviewers: #kwin, #plasma, subdiff

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D8602

plugins/platforms/drm/drm_object_plane.cpp

@@ -125,6 +125,11 @@ void DrmPlane::setTransformation(Transformations t)
     setValue(int(PropertyIndex::Rotation), int(t));
 }
 
+DrmPlane::Transformations DrmPlane::transformation()
+{
+    return Transformations(int(value(int(PropertyIndex::Rotation))));
+}
+
 bool DrmPlane::atomicPopulate(drmModeAtomicReq *req)
 {
     bool ret = true;

plugins/platforms/drm/drm_object_plane.h

@@ -91,6 +91,7 @@ public:
     }
     void setNext(DrmBuffer *b);
     void setTransformation(Transformations t);
+    Transformations transformation();
 
     bool atomicPopulate(drmModeAtomicReq *req);
     void flipBuffer();

plugins/platforms/drm/drm_output.cpp

@@ -804,7 +804,6 @@ void DrmOutput::updateMode(int modeIndex)
         // nothing to do
         return;
     }
-    m_previousMode = m_mode;
     m_mode = connector->modes[modeIndex];
     m_modesetRequested = true;
     emit modeChanged();
@@ -909,13 +908,37 @@ bool DrmOutput::presentAtomically(DrmBuffer *buffer)
         //TODO: When we use planes for layered rendering, fallback to renderer instead. Also for direct scanout?
         //TODO: Probably should undo setNext and reset the flip list
         qCDebug(KWIN_DRM) << "Atomic test commit failed. Aborting present.";
+        // go back to previous state
+        if (m_lastWorkingState.valid) {
+            m_mode = m_lastWorkingState.mode;
+            m_orientation = m_lastWorkingState.orientation;
+            setGlobalPos(m_lastWorkingState.globalPos);
+            if (m_primaryPlane) {
+                m_primaryPlane->setTransformation(m_lastWorkingState.planeTransformations);
+            }
+            m_modesetRequested = true;
+            // TODO: forward to OutputInterface and OutputDeviceInterface
+            emit modeChanged();
+            emit screens()->changed();
+        }
         return false;
     }
+    const bool wasModeset = m_modesetRequested;
     if (!doAtomicCommit(AtomicCommitMode::Real)) {
         qCDebug(KWIN_DRM) << "Atomic commit failed. This should have never happened! Aborting present.";
         //TODO: Probably should undo setNext and reset the flip list
         return false;
     }
+    if (wasModeset) {
+        // store current mode set as new good state
+        m_lastWorkingState.mode = m_mode;
+        m_lastWorkingState.orientation = m_orientation;
+        m_lastWorkingState.globalPos = m_globalPos;
+        if (m_primaryPlane) {
+            m_lastWorkingState.planeTransformations = m_primaryPlane->transformation();
+        }
+        m_lastWorkingState.valid = true;
+    }
     m_pageFlipPending = true;
     return true;
 }

plugins/platforms/drm/drm_output.h

@@ -22,6 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include "drm_pointer.h"
 #include "drm_object.h"
+#include "drm_object_plane.h"
 
 #include <QObject>
 #include <QPoint>
@@ -147,7 +148,6 @@ private:
     qreal m_scale = 1;
     bool m_lastGbm = false;
     drmModeModeInfo m_mode;
-    drmModeModeInfo m_previousMode;
     Edid m_edid;
     QPointer<KWayland::Server::OutputInterface> m_waylandOutput;
     QPointer<KWayland::Server::OutputDeviceInterface> m_waylandOutputDevice;
@@ -166,6 +166,14 @@ private:
     bool m_modesetRequested = true;
     QSize m_physicalSize;
     Qt::ScreenOrientation m_orientation = Qt::PrimaryOrientation;
+
+    struct {
+        Qt::ScreenOrientation orientation;
+        drmModeModeInfo mode;
+        DrmPlane::Transformations planeTransformations;
+        QPoint globalPos;
+        bool valid = false;
+    } m_lastWorkingState;
 };
 
 }