ASoC: apple: mca: Constrain channels according to TDM mask

We don't (and can't) configure the hardware correctly if the number of
channels exceeds the weight of the TDM mask. Report that constraint in
startup of FE.

Fixes: 3df5d0d ("ASoC: apple: mca: Start new platform driver")
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Signed-off-by: James Calligeros <jcalligeros99@gmail.com>
Link: https://patch.msgid.link/20250518-mca-fixes-v1-1-ee1015a695f6@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: povik

sound/soc/apple/mca.c

@@ -464,6 +464,28 @@ static int mca_configure_serdes(struct mca_cluster *cl, int serdes_unit,
 	return -EINVAL;
 }
 
+static int mca_fe_startup(struct snd_pcm_substream *substream,
+			  struct snd_soc_dai *dai)
+{
+	struct mca_cluster *cl = mca_dai_to_cluster(dai);
+	unsigned int mask, nchannels;
+
+	if (cl->tdm_slots) {
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			mask = cl->tdm_tx_mask;
+		else
+			mask = cl->tdm_rx_mask;
+
+		nchannels = hweight32(mask);
+	} else {
+		nchannels = 2;
+	}
+
+	return snd_pcm_hw_constraint_minmax(substream->runtime,
+					    SNDRV_PCM_HW_PARAM_CHANNELS,
+					    1, nchannels);
+}
+
 static int mca_fe_set_tdm_slot(struct snd_soc_dai *dai, unsigned int tx_mask,
 			       unsigned int rx_mask, int slots, int slot_width)
 {
@@ -680,6 +702,7 @@ static int mca_fe_hw_params(struct snd_pcm_substream *substream,
 }
 
 static const struct snd_soc_dai_ops mca_fe_ops = {
+	.startup = mca_fe_startup,
 	.set_fmt = mca_fe_set_fmt,
 	.set_bclk_ratio = mca_set_bclk_ratio,
 	.set_tdm_slot = mca_fe_set_tdm_slot,