Similarly to invalidating beforehand, if the object is mmapped via
I915_MMAP_WC we cannot track writes through the I915_GEM_DOMAIN_GTT. At
the conclusion of the write, i915_gem_object_flush_gtt_writes() we also
need to treat the origin carefully in case it may have been untracked.
See also commit 
aeecc9696aa0 ("drm/i915: use ORIGIN_CPU for frontbuffer
invalidation on WC mmaps").
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160818161718.27187-5-chris@chris-wilson.co.uk
        return ret;
 }
 
-static enum fb_op_origin
+static inline enum fb_op_origin
 write_origin(struct drm_i915_gem_object *obj, unsigned domain)
 {
        return domain == I915_GEM_DOMAIN_GTT && !obj->has_wc_mmap ?
        old_write_domain = obj->base.write_domain;
        obj->base.write_domain = 0;
 
-       intel_fb_obj_flush(obj, false, ORIGIN_GTT);
+       intel_fb_obj_flush(obj, false, write_origin(obj, I915_GEM_DOMAIN_GTT));
 
        trace_i915_gem_object_change_domain(obj,
                                            obj->base.read_domains,