simple_callback
if (dma_fence_add_callback(f, &cb.cb, simple_callback)) {
if (!dma_fence_add_callback(f, &cb.cb, simple_callback)) {
if (dma_fence_add_callback(f, &cb.cb, simple_callback)) {
if (dma_fence_add_callback(f, &cb.cb, simple_callback)) {
dma_fence_add_callback(f2, &cb.cb, simple_callback)) {
pipe, length, transfer_flags, 1, 0, simple_callback);
bInterval, simple_callback);