backends/drm: support link-status

Userspace is expected to do a modeset and set link-status to good again,
if link-status gets bad. This is needed to prevent some black screen situations.

BUG: 448177

src/backends/drm/drm_object_connector.cpp

@@ -101,6 +101,10 @@ DrmConnector::DrmConnector(DrmGpu *gpu, uint32_t connectorId)
                 QByteArrayLiteral("Limited 16:235")
             }),
             PropertyDefinition(QByteArrayLiteral("max bpc"), Requirement::Optional),
+            PropertyDefinition(QByteArrayLiteral("link-status"), Requirement::Optional, {
+                QByteArrayLiteral("Good"),
+                QByteArrayLiteral("Bad")
+            }),
         }, DRM_MODE_OBJECT_CONNECTOR)
     , m_pipeline(new DrmPipeline(this))
     , m_conn(drmModeGetConnector(gpu->fd(), connectorId))
@@ -421,6 +425,14 @@ void DrmConnector::disable()
     setPending(PropertyIndex::CrtcId, 0);
 }
 
+DrmConnector::LinkStatus DrmConnector::linkStatus() const
+{
+    if (const auto &property = getProp(PropertyIndex::LinkStatus)) {
+        return property->enumForValue<LinkStatus>(property->current());
+    }
+    return LinkStatus::Good;
+}
+
 QDebug& operator<<(QDebug& s, const KWin::DrmConnector *obj)
 {
     QDebugStateSaver saver(s);

src/backends/drm/drm_object_connector.h

@@ -66,6 +66,7 @@ public:
         Underscan_hborder = 8,
         Broadcast_RGB = 9,
         MaxBpc = 10,
+        LinkStatus = 11,
         Count
     };
 
@@ -74,6 +75,10 @@ public:
         On = 1,
         Auto = 2,
     };
+    enum class LinkStatus : uint32_t {
+        Good = 0,
+        Bad = 1
+    };
 
     bool init() override;
     bool needsModeset() const override;
@@ -105,6 +110,7 @@ public:
     bool vrrCapable() const;
     bool hasRgbRange() const;
     AbstractWaylandOutput::RgbRange rgbRange() const;
+    LinkStatus linkStatus() const;
 
 private:
     QScopedPointer<DrmPipeline> m_pipeline;

src/backends/drm/drm_pipeline.cpp

@@ -230,6 +230,9 @@ void DrmPipeline::prepareAtomicModeset()
     if (const auto &prop = m_connector->getProp(DrmConnector::PropertyIndex::Broadcast_RGB)) {
         prop->setEnum(pending.rgbRange);
     }
+    if (const auto &prop = m_connector->getProp(DrmConnector::PropertyIndex::LinkStatus)) {
+        prop->setEnum(DrmConnector::LinkStatus::Good);
+    }
 
     pending.crtc->setPending(DrmCrtc::PropertyIndex::Active, activePending());
     pending.crtc->setPending(DrmCrtc::PropertyIndex::ModeId, activePending() ? mode->blobId() : 0);
@@ -501,6 +504,7 @@ bool DrmPipeline::needsModeset() const
         || pending.modeIndex != m_current.modeIndex
         || pending.rgbRange != m_current.rgbRange
         || pending.bufferTransformation != m_current.bufferTransformation
+        || m_connector->linkStatus() == DrmConnector::LinkStatus::Bad
         || m_modesetPresentPending;
 }