This is now used intentionally to prevent proliferation of is-pinned
checks upon the inactive list following:
commit 
1b50247a8ddde4af5aaa0e6bc125615372ce6c16
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Apr 24 15:47:30 2012 +0100
    drm/i915: Remove the list of pinned inactive objects
Reported-and-tested-by: guang.a.yang@intel.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50075
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
 
        if (obj->gtt_space == NULL)
                return 0;
 
-       if (obj->pin_count != 0) {
-               DRM_ERROR("Attempting to unbind pinned buffer\n");
-               return -EINVAL;
-       }
+       if (obj->pin_count)
+               return -EBUSY;
 
        ret = i915_gem_object_finish_gpu(obj);
        if (ret)