platformsupport/scenes/opengl: use the render node for dmabuf feedback

It gives applications better information about what render device to use, and also
works around issues in Xwayland and some broken drivers

src/opengl/egldisplay.cpp

@@ -7,6 +7,7 @@
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 #include "egldisplay.h"
+#include "core/drmdevice.h"
 #include "core/graphicsbuffer.h"
 #include "opengl/eglutils_p.h"
 #include "opengl/glutils.h"
@@ -73,11 +74,23 @@ std::unique_ptr<EglDisplay> EglDisplay::create(::EGLDisplay display, bool owning
     return std::make_unique<EglDisplay>(display, extensions, owning);
 }
 
+static std::optional<dev_t> devIdForFileName(const QString &path)
+{
+    auto device = DrmDevice::open(path);
+    if (device) {
+        return device->deviceId();
+    } else {
+        qCWarning(KWIN_OPENGL, "couldn't find dev node for drm device %s", qPrintable(path));
+        return std::nullopt;
+    }
+}
+
 EglDisplay::EglDisplay(::EGLDisplay display, const QList<QByteArray> &extensions, bool owning)
     : m_handle(display)
     , m_extensions(extensions)
     , m_owning(owning)
     , m_renderNode(determineRenderNode())
+    , m_renderDevNode(devIdForFileName(m_renderNode))
     , m_supportsBufferAge(extensions.contains(QByteArrayLiteral("EGL_EXT_buffer_age")) && qgetenv("KWIN_USE_BUFFER_AGE") != "0")
     , m_supportsNativeFence(extensions.contains(QByteArrayLiteral("EGL_ANDROID_native_fence_sync")))
 {
@@ -334,6 +347,11 @@ QString EglDisplay::determineRenderNode() const
     return QString();
 }
 
+std::optional<dev_t> EglDisplay::renderDevNode() const
+{
+    return m_renderDevNode;
+}
+
 EGLImageKHR EglDisplay::createImage(EGLContext ctx, EGLenum target, EGLClientBuffer buffer, const EGLint *attrib_list) const
 {
     Q_ASSERT(m_functions.createImageKHR);

src/opengl/egldisplay.h

@@ -40,6 +40,7 @@ public:
     bool hasExtension(const QByteArray &name) const;
 
     QString renderNode() const;
+    std::optional<dev_t> renderDevNode() const;
 
     bool supportsBufferAge() const;
     bool supportsNativeFence() const;
@@ -65,6 +66,7 @@ private:
     const QList<QByteArray> m_extensions;
     const bool m_owning;
     const QString m_renderNode;
+    const std::optional<dev_t> m_renderDevNode;
 
     const bool m_supportsBufferAge;
     const bool m_supportsNativeFence;

src/platformsupport/scenes/opengl/abstract_egl_backend.cpp

@@ -174,17 +174,17 @@ void AbstractEglBackend::initWayland()
         };
 
         m_tranches.append({
-            .device = scanoutDevice->deviceId(),
+            .device = m_display->renderDevNode().value_or(scanoutDevice->deviceId()),
             .flags = {},
             .formatTable = filterFormats(10, false),
         });
         m_tranches.append({
-            .device = scanoutDevice->deviceId(),
+            .device = m_display->renderDevNode().value_or(scanoutDevice->deviceId()),
             .flags = {},
             .formatTable = filterFormats(8, false),
         });
         m_tranches.append({
-            .device = scanoutDevice->deviceId(),
+            .device = m_display->renderDevNode().value_or(scanoutDevice->deviceId()),
             .flags = {},
             .formatTable = includeShaderConversions(filterFormats({}, true)),
         });