in core.c [300:319]
static int __mux_control_select(struct mux_control *mux, int state)
{
int ret;
if (WARN_ON(state < 0 || state >= mux->states))
return -EINVAL;
if (mux->cached_state == state)
return 0;
ret = mux_control_set(mux, state);
if (ret >= 0)
return 0;
/* The mux update failed, try to revert if appropriate... */
if (mux->idle_state != MUX_IDLE_AS_IS)
mux_control_set(mux, mux->idle_state);
return ret;
}