write_active
applespi->write_active = false;
wait_event_lock_irq(applespi->drain_complete, !applespi->write_active,
applespi->write_active = false;
bool write_active;
applespi->write_active = false;
if (applespi->drain && !applespi->write_active)
applespi->write_active = false;
applespi->write_active = true;
write_active(active);