platforms/drm: Fix initialization of EGL displays

Currently, every time compositing is restarted, both the gbm and the egl
streams backend will re-obtain the EGLDisplay object.

This is wrong because the core assumption is that the EGL display doesn't
change once it has been obtained.

plugins/platforms/drm/drm_gpu.h

@@ -13,6 +13,9 @@
 #include <qobject.h>
 #include <QVector>
 
+#include <epoxy/egl.h>
+#include <fixx11h.h>
+
 #include "drm_buffer.h"
 
 struct gbm_device;
@@ -58,6 +61,10 @@ public:
     gbm_device *gbmDevice() const {
         return m_gbmDevice;
     }
+
+    EGLDisplay eglDisplay() const {
+        return m_eglDisplay;
+    }
     
     QVector<DrmPlane*> planes() const {
         return m_planes;
@@ -66,6 +73,10 @@ public:
     void setGbmDevice(gbm_device *d) {
         m_gbmDevice = d;
     }
+
+    void setEglDisplay(EGLDisplay display) {
+        m_eglDisplay = display;
+    }
     
     DrmDumbBuffer *createBuffer(const QSize &size) const {
         return new DrmDumbBuffer(m_fd, size);
@@ -95,6 +106,7 @@ private:
     bool m_atomicModeSetting;
     bool m_useEglStreams;
     gbm_device* m_gbmDevice;
+    EGLDisplay m_eglDisplay = EGL_NO_DISPLAY;
     
 // all available planes: primarys, cursors and overlays
     QVector<DrmPlane*> m_planes;

plugins/platforms/drm/egl_gbm_backend.cpp

@@ -74,7 +74,7 @@ void EglGbmBackend::cleanupOutput(Output &output)
 bool EglGbmBackend::initializeEgl()
 {
     initClientExtensions();
-    EGLDisplay display = eglDisplay();
+    EGLDisplay display = m_gpu->eglDisplay();
 
     // Use eglGetPlatformDisplayEXT() to get the display pointer
     // if the implementation supports it.
@@ -98,6 +98,7 @@ bool EglGbmBackend::initializeEgl()
         m_gpu->setGbmDevice(device);
 
         display = eglGetPlatformDisplayEXT(platform, device, nullptr);
+        m_gpu->setEglDisplay(display);
     }
 
     if (display == EGL_NO_DISPLAY) {

plugins/platforms/drm/egl_stream_backend.cpp

@@ -121,7 +121,7 @@ void EglStreamBackend::cleanupOutput(const Output &o)
 bool EglStreamBackend::initializeEgl()
 {
     initClientExtensions();
-    EGLDisplay display = eglDisplay();
+    EGLDisplay display = m_gpu->eglDisplay();
     if (display == EGL_NO_DISPLAY) {
         if (!hasClientExtension(QByteArrayLiteral("EGL_EXT_device_base")) &&
             !(hasClientExtension(QByteArrayLiteral("EGL_EXT_device_query")) &&
@@ -157,6 +157,7 @@ bool EglStreamBackend::initializeEgl()
             display = eglGetPlatformDisplayEXT(EGL_PLATFORM_DEVICE_EXT, device, platformAttribs);
             break;
         }
+        m_gpu->setEglDisplay(display);
     }
 
     if (display == EGL_NO_DISPLAY) {