chn_polltrigger
if (SEL_WAITING(&bs->sel) && chn_polltrigger(c, bs->prev_total))
if (chn_polltrigger(c, bs->prev_total)) {
int chn_polltrigger(struct pcm_channel *c, uint64_t ref_total);
if (chn_polltrigger(ch, (uint64_t)kn->kn_sdata)) {