Since devices that can't DMA above 4GiB will misbehave with this option enabled add a warning on the documentation. Reviewed-by: Simon Glass <sjg@chromium.org> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Tested-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>