ASoC: pcm: do no 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

@@ -3111,7 +3111,9 @@ int soc_new_pcm(struct snd_soc_pcm_runtime *rtd, int num)
 	struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
 	struct snd_soc_component *component;
 	struct snd_soc_rtdcom_list *rtdcom;
+	struct snd_pcm_substream *substream;
 	struct snd_pcm *pcm;
+	int stream_dir;
 	char new_name[64];
 	int ret = 0, playback = 0, capture = 0;
 	int i;
@@ -3150,6 +3152,44 @@ 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 {
+
+		/*
+		 * for virtual FE dai links, there is no need
+		 * to register PCM device. So only allocate memory for
+		 * pcm device and substream for the requested direction
+		 */
+		if (rtd->dai_link->virtual) {
+			struct snd_pcm_str *pstr;
+
+			if (rtd->dai_link->dpcm_playback)
+				stream_dir = SNDRV_PCM_STREAM_PLAYBACK;
+
+			pcm = kzalloc(sizeof(*pcm), GFP_KERNEL);
+			if (!pcm)
+				return -ENOMEM;
+
+			pstr = &pcm->streams[stream_dir];
+
+			substream = kzalloc(sizeof(*substream), GFP_KERNEL);
+			if (!substream)
+				return -ENOMEM;
+
+			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;
+
+			pstr->substream = substream;
+
+			pcm->nonatomic = rtd->dai_link->nonatomic;
+			rtd->pcm = pcm;
+			pcm->private_data = rtd;
+
+			goto out;
+		}
+
 		if (rtd->dai_link->dynamic)
 			snprintf(new_name, sizeof(new_name), "%s (*)",
 				rtd->dai_link->stream_name);