sndbuf_runsz
i = (sndbuf_runsz(ch->buffer) >> ((bits & 0x08)? 1 : 0)) - 1;
tr_wr(tr, TR_REG_DMAR4, i | (sndbuf_runsz(ch->buffer) - 1), 4);
unsigned int sndbuf_runsz(struct snd_dbuf *b);