Comment 70 for bug 1040873

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/?id=ee81abb623cb5e03c182d16871bb4fb34fdc9b4f

do you need a new mapping

map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR,
+ SNDRV_CHMAP_NA, SNDRV_CHMAP_LFE

or use the default 2.1

+/* default channel maps for 2.1 speakers;
+ * since HD-audio supports only stereo, odd number channels are omitted
+ */
+const struct snd_pcm_chmap_elem snd_pcm_2_1_chmaps[] = {
+ { .channels = 2,
+ .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR } },
+ { .channels = 4,
+ .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR,
+ SNDRV_CHMAP_LFE, SNDRV_CHMAP_LFE } },
+ { }
+};