ASoC: pcm: do not register pcm device for virtual FE dai links

Virtual FE dai links do not need to register the pcm device. So
just create the empty pcm device and substream in the
requested direction.

Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>

sound/soc/soc-pcm.c

@@ -3098,6 +3098,55 @@ static int soc_rtdcom_mmap(struct snd_pcm_substream *substream,
 	return -EINVAL;
 }
 
+/*
+ * for virtual FE dai links, there is no need
+ * to register PCM device. So only allocate memory for
+ * the dummy pcm device and substreams to be used for
+ * codec startup
+ */
+static int setup_virtual_fe(struct snd_soc_pcm_runtime *rtd,
+			    struct snd_pcm *pcm)
+{
+	struct snd_pcm_substream *substream;
+	struct snd_pcm_str *pstr;
+	int stream_dir;
+
+	/* create pcm */
+	pcm = kzalloc(sizeof(*pcm), GFP_KERNEL);
+	if (!pcm)
+		return -ENOMEM;
+
+	/* set up playback/capture substream */
+	if (rtd->dai_link->dpcm_playback)
+		stream_dir = SNDRV_PCM_STREAM_PLAYBACK;
+	else
+		stream_dir = SNDRV_PCM_STREAM_CAPTURE;
+
+	pstr = &pcm->streams[stream_dir];
+
+	/* allocate memory for substream */
+	substream = kzalloc(sizeof(*substream), GFP_KERNEL);
+	if (!substream)
+		return -ENOMEM;
+
+	/* define substream */
+	substream->pcm = pcm;
+	substream->pstr = pstr;
+	substream->number = 0;
+	substream->stream = stream_dir;
+	sprintf(substream->name, "subdevice #%i", 0);
+	substream->buffer_bytes_max = UINT_MAX;
+
+	/* set pcm substream */
+	pstr->substream = substream;
+
+	pcm->nonatomic = rtd->dai_link->nonatomic;
+	rtd->pcm = pcm;
+	pcm->private_data = rtd;
+
+	return 0;
+}
+
 /* create a new pcm */
 int soc_new_pcm(struct snd_soc_pcm_runtime *rtd, int num)
 {
@@ -3145,6 +3194,13 @@ int soc_new_pcm(struct snd_soc_pcm_runtime *rtd, int num)
 		ret = snd_pcm_new_internal(rtd->card->snd_card, new_name, num,
 				playback, capture, &pcm);
 	} else {
+
+		/* set up virtual FE dai link */
+		if (rtd->dai_link->dynamic && rtd->dai_link->no_pcm) {
+			setup_virtual_fe(rtd, pcm);
+			goto out;
+		}
+
 		if (rtd->dai_link->dynamic)
 			snprintf(new_name, sizeof(new_name), "%s (*)",
 				rtd->dai_link->stream_name);