ASoC: audio-graph: Support empty Codec endpoint

For open platforms, which can support pluggable audio cards, Codec
endpoint is not fixed always. It actually depends on the compatible
HW module that is going to be connected. From SoC side the given I/O
interface is always available. Hence such links have fixed CPU endpoint
but no Codec endpoint. This patch helps to support such links where
user can populate Codec endpoint only and its fields in Platform DT
depending on the plugged HW.
Signed-off-by: Sameer Pujar <spujar@nvidia.com>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/1604329814-24779-6-git-send-email-spujar@nvidia.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/generic/audio-graph-card.c

@@ -229,6 +229,14 @@ static int graph_dai_link_of_dpcm(struct asoc_simple_priv *priv,
 	struct snd_soc_dai_link_component *codecs = dai_link->codecs;
 	int ret;
 
+	/*
+	 * Codec endpoint can be NULL for pluggable audio HW.
+	 * Platform DT can populate the Codec endpoint depending on the
+	 * plugged HW.
+	 */
+	if (!li->cpu && !codec_ep)
+		return 0;
+
 	/* Do it all CPU endpoint, and 1st Codec endpoint */
 	if (!li->cpu && dup_codec)
 		return 0;
@@ -565,7 +573,7 @@ static int graph_count_dpcm(struct asoc_simple_priv *priv,
 	li->link++; /* 1xCPU-dummy */
 	li->dais++; /* 1xCPU */
 
-	if (!dup_codec) {
+	if (!dup_codec && codec_ep) {
 		li->link++; /* 1xdummy-Codec */
 		li->conf++; /* 1xdummy-Codec */
 		li->dais++; /* 1xCodec */