ASoC: bdw-rt5677: add channel constraint

BDW boards using this machine driver supports only stereo capture and
playback. Implement a constraint to enforce it.
Signed-off-by: Brent Lu <brent.lu@intel.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/1588007614-25061-2-git-send-email-brent.lu@intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/intel/boards/bdw-rt5677.c

@@ -222,6 +222,31 @@ static int bdw_rt5677_rtd_init(struct snd_soc_pcm_runtime *rtd)
 }
 #endif
 
+static const unsigned int channels[] = {
+	2,
+};
+
+static const struct snd_pcm_hw_constraint_list constraints_channels = {
+	.count = ARRAY_SIZE(channels),
+	.list = channels,
+	.mask = 0,
+};
+
+static int bdw_rt5677_fe_startup(struct snd_pcm_substream *substream)
+{
+	struct snd_pcm_runtime *runtime = substream->runtime;
+
+	/* Board supports stereo configuration only */
+	runtime->hw.channels_max = 2;
+	return snd_pcm_hw_constraint_list(runtime, 0,
+					  SNDRV_PCM_HW_PARAM_CHANNELS,
+					  &constraints_channels);
+}
+
+static const struct snd_soc_ops bdw_rt5677_fe_ops = {
+	.startup = bdw_rt5677_fe_startup,
+};
+
 static int bdw_rt5677_init(struct snd_soc_pcm_runtime *rtd)
 {
 	struct bdw_rt5677_priv *bdw_rt5677 =
@@ -321,6 +346,7 @@ static struct snd_soc_dai_link bdw_rt5677_dais[] = {
 		},
 		.dpcm_capture = 1,
 		.dpcm_playback = 1,
+		.ops = &bdw_rt5677_fe_ops,
 		SND_SOC_DAILINK_REG(fe, dummy, platform),
 	},