[mutter] renderer/native: Count devices on EGLDevice check

[Jonas Ådahl <jadahl src gnome org>]

commit 3d2ca9a67f6d2c7399f50f89c54d6ea4f86c58f0
Author: Pekka Paalanen <pekka paalanen collabora com>
Date:   Mon Dec 10 15:46:56 2018 +0200

    renderer/native: Count devices on EGLDevice check
    
    create_renderer_gpu_data_egl_device () relied on the primary GPU being
    already chosen for the "EGLDevice currently only works with single GPU
    systems" error message. A future patch will choose the primary GPU after
    this, not before, so this check needs to be rewritten before the
    initialization order is changed.
    
    The new check is implemented exactly as the error message says: there
    must be exactly one GPU, otherwise fail.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/271

 src/backends/native/meta-renderer-native.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index 4a514dce9..553e79b69 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -3447,6 +3447,15 @@ get_egl_device_display (MetaRendererNative  *renderer_native,
                                         error);
 }
 
+static int
+count_drm_devices (MetaRendererNative *renderer_native)
+{
+  MetaMonitorManager *monitor_manager =
+    META_MONITOR_MANAGER (renderer_native->monitor_manager_kms);
+
+  return g_list_length (meta_monitor_manager_get_gpus (monitor_manager));
+}
+
 static MetaRendererNativeGpuData *
 create_renderer_gpu_data_egl_device (MetaRendererNative  *renderer_native,
                                      MetaGpuKms          *gpu_kms,
@@ -3458,7 +3467,7 @@ create_renderer_gpu_data_egl_device (MetaRendererNative  *renderer_native,
   EGLDisplay egl_display;
   MetaRendererNativeGpuData *renderer_gpu_data;
 
-  if (gpu_kms != renderer_native->primary_gpu)
+  if (count_drm_devices (renderer_native) != 1)
     {
       g_set_error (error, G_IO_ERROR,
                    G_IO_ERROR_FAILED,