[mutter] renderer/native: check format for drmModeAddFB fallback

[Jonas Ådahl <jadahl src gnome org>]

commit 3e1ca62782043e3d58d21c205a217624e72faf9c
Author: Pekka Paalanen <pekka paalanen collabora co uk>
Date:   Wed Sep 5 10:38:09 2018 +0300

    renderer/native: check format for drmModeAddFB fallback
    
    If drmModeAddFB2() does not work, the fallback to drmModeAddFB() can
    only handle a single specific format. Make sure the requested format is
    that one format, and fail the operation otherwise.
    
    This should at least makes the failure mode obvious on such old systems
    where the kernel does not support AddFB2, rather than producing wrong
    colors.

 src/backends/native/meta-renderer-native.c | 10 ++++++++++
 1 file changed, 10 insertions(+)
---
diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index 08b9befbb..6eaa0b45f 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -3,6 +3,7 @@
 /*
  * Copyright (C) 2011 Intel Corporation.
  * Copyright (C) 2016 Red Hat
+ * Copyright (c) 2018 DisplayLink (UK) Ltd.
  *
  * Permission is hereby granted, free of charge, to any person
  * obtaining a copy of this software and associated documentation
@@ -2246,6 +2247,15 @@ init_dumb_fb (MetaDumbBuffer  *dumb_fb,
 
   if (fb_id == 0)
     {
+      if (format != DRM_FORMAT_XRGB8888)
+        {
+          g_set_error (error, G_IO_ERROR,
+                       G_IO_ERROR_FAILED,
+                       "drmModeAddFB does not support format 0x%x",
+                       format);
+          goto err_add_fb;
+        }
+
       if (drmModeAddFB (kms_fd, width, height,
                         24 /* depth of RGBX8888 */,
                         32 /* bpp of RGBX8888 */,