pcm_getparentchannel
pcm_getparentchannel(d, &c, NULL);
pcm_getparentchannel(d, NULL, &c);
pcm_getparentchannel(d, &c, NULL);
pcm_getparentchannel(d, NULL, &c);
pcm_getparentchannel(d, &c, NULL);
pcm_getparentchannel(d, NULL, &c);