The 4.15 drm_atomic_helper driver shows a warning during boot (both 32 
and 64 bit x86)
It is caused by a mismatch between the result of vmw_enable_vblank() and 
what the drm_atomic_helper expects:
    /...
    ret = drm_crtc_vblank_get(crtc);
    WARN_ONCE(ret != -EINVAL, "driver forgot to call 
drm_crtc_vblank_off()\n");
    /...

Signed-off by: Woody Suwalski <terraluna977@gmail.com>

--- a/drivers/gpu/drm/drm_atomic_helper.c    2017-12-16 
09:55:33.853374561 -0500
+++ b/drivers/gpu/drm/drm_atomic_helper.c    2017-12-16 
10:55:56.089090752 -0500
@@ -889,7 +889,7 @@ disable_outputs(struct drm_device *dev,
              continue;

          ret = drm_crtc_vblank_get(crtc);
-        WARN_ONCE(ret != -EINVAL, "driver forgot to call 
drm_crtc_vblank_off()\n");
+        WARN_ONCE((ret != -EINVAL && ret != -ENOSYS), "driver forgot to 
call drm_crtc_vblank_off()\n");
          if (ret == 0)
              drm_crtc_vblank_put(crtc);
      }