i915_gem_object_prepare_read
int i915_gem_object_prepare_read(struct drm_i915_gem_object *obj,
err = i915_gem_object_prepare_read(obj, &needs_flush);
err = i915_gem_object_prepare_read(ctx->obj, &needs_clflush);
err = i915_gem_object_prepare_read(obj, &needs_flush);
ret = i915_gem_object_prepare_read(src_obj, &src_needs_clflush);
ret = i915_gem_object_prepare_read(obj, &needs_clflush);