[mutter] renderer-native: Fall back to non-modifier GBM surfaces

[Jonas Ådahl <jadahl src gnome org>]

commit e6109cfc22f06412e67bd3c1f9f0dfa6ad7e0b19
Author: Daniel Stone <daniels collabora com>
Date:   Mon Apr 2 17:14:53 2018 +0100

    renderer-native: Fall back to non-modifier GBM surfaces
    
    If we attempt GBM surface allocation with a set of modifiers but the
    allocation fails, fall back to non-modifier allocations. This fixes
    startup on Pineview-based Atom systems, where KMS provides us a set of
    modifiers but the GBM implementation doesn't support modifier use.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/issues/84

 src/backends/native/meta-renderer-native.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index 1fc593ad5..2717f7d2e 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -1996,7 +1996,7 @@ meta_renderer_native_create_surface_gbm (CoglOnscreen        *onscreen,
   CoglRenderer *cogl_renderer = cogl_display->renderer;
   CoglRendererEGL *cogl_renderer_egl = cogl_renderer->winsys;
   MetaRendererNativeGpuData *renderer_gpu_data = cogl_renderer_egl->platform;
-  struct gbm_surface *new_gbm_surface;
+  struct gbm_surface *new_gbm_surface = NULL;
   EGLNativeWindowType egl_native_window;
   EGLSurface new_egl_surface;
   uint32_t format = GBM_FORMAT_XRGB8888;
@@ -2017,7 +2017,8 @@ meta_renderer_native_create_surface_gbm (CoglOnscreen        *onscreen,
                                            modifiers->len);
       g_array_free (modifiers, TRUE);
     }
-  else
+
+  if (!new_gbm_surface)
     {
       uint32_t flags = GBM_BO_USE_SCANOUT | GBM_BO_USE_RENDERING;