ASoC: bdw-rt5650: add channel constraint

BDW boards using this machine driver supports only 2 or 4-channel capture.
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/1588007614-25061-3-git-send-email-brent.lu@intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/intel/boards/bdw-rt5650.c

@@ -162,6 +162,34 @@ static int bdw_rt5650_rtd_init(struct snd_soc_pcm_runtime *rtd)
 }
 #endif
 
+static const unsigned int channels[] = {
+	2, 4,
+};
+
+static const struct snd_pcm_hw_constraint_list constraints_channels = {
+	.count = ARRAY_SIZE(channels),
+	.list = channels,
+	.mask = 0,
+};
+
+static int bdw_rt5650_fe_startup(struct snd_pcm_substream *substream)
+{
+	struct snd_pcm_runtime *runtime = substream->runtime;
+
+	/* Board supports stereo and quad configurations for capture */
+	if (substream->stream != SNDRV_PCM_STREAM_CAPTURE)
+		return 0;
+
+	runtime->hw.channels_max = 4;
+	return snd_pcm_hw_constraint_list(runtime, 0,
+					  SNDRV_PCM_HW_PARAM_CHANNELS,
+					  &constraints_channels);
+}
+
+static const struct snd_soc_ops bdw_rt5650_fe_ops = {
+	.startup = bdw_rt5650_fe_startup,
+};
+
 static int bdw_rt5650_init(struct snd_soc_pcm_runtime *rtd)
 {
 	struct bdw_rt5650_priv *bdw_rt5650 =
@@ -234,6 +262,7 @@ static struct snd_soc_dai_link bdw_rt5650_dais[] = {
 		.name = "System PCM",
 		.stream_name = "System Playback",
 		.dynamic = 1,
+		.ops = &bdw_rt5650_fe_ops,
 #if !IS_ENABLED(CONFIG_SND_SOC_SOF_BROADWELL)
 		.init = bdw_rt5650_rtd_init,
 #endif