[mutter] kms/plane: Make get_primary_plane() actually get the primary plane

[Marge Bot <marge-bot src gnome org>]

commit 6bda72e3eb241c5eee41143ff708b58deb546c4b
Author: Jonas Ådahl <jadahl gmail com>
Date:   Fri Oct 9 22:06:19 2020 +0200

    kms/plane: Make get_primary_plane() actually get the primary plane
    
    The plane was not type checked, so it retrieved whatever plane happened
    to come first.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1488>

 src/backends/native/meta-kms-update.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/src/backends/native/meta-kms-update.c b/src/backends/native/meta-kms-update.c
index 95f480bccc..9d32a0da29 100644
--- a/src/backends/native/meta-kms-update.c
+++ b/src/backends/native/meta-kms-update.c
@@ -466,8 +466,14 @@ meta_kms_update_get_primary_plane_assignment (MetaKmsUpdate *update,
     {
       MetaKmsPlaneAssignment *plane_assignment = l->data;
 
-      if (plane_assignment->crtc == crtc)
-        return plane_assignment;
+      if (meta_kms_plane_get_plane_type (plane_assignment->plane) !=
+          META_KMS_PLANE_TYPE_PRIMARY)
+        continue;
+
+      if (plane_assignment->crtc != crtc)
+        continue;
+
+      return plane_assignment;
     }
 
   return NULL;