Introducing Virtual FE dai link

include/sound/soc-dpcm.h

@@ -158,5 +158,8 @@ static inline void dpcm_path_put(struct snd_soc_dapm_widget_list **list)
 	kfree(*list);
 }
 
-
+/* create/free virtual FE dai links */
+int soc_dpcm_vfe_new(struct snd_soc_card *, int index, const char *link_name,
+		     const char *cpu_dai_name, const char *platform_name);
+int soc_dpcm_vfe_free(struct snd_soc_card *card);
 #endif

include/sound/soc.h

@@ -1134,6 +1134,17 @@ struct snd_soc_dai_link {
 	/* Do not create a PCM for this DAI link (Backend link) */
 	unsigned int ignore:1;
 
+	/*
+	 * virtual FE link
+	 * This flag indicates that there is no PCM device registered with ALSA
+	 * This is intended to be used for establishing a connection to the
+	 * BE DAI in the case of hostless pipelines such as,
+	 * DSP component -> codec, ex: tone generator -> codec
+	 * This connection will be established at runtime by triggering the
+	 * hostless pipeline with a kcontrol attached to the component.
+	 */
+	unsigned int virtual:1;
+
 	struct list_head list; /* DAI link list of the soc card */
 	struct snd_soc_dobj dobj; /* For topology */
 };

sound/soc/soc-core.c

@@ -1047,6 +1047,7 @@ static int soc_bind_dai_link(struct snd_soc_card *card,
 	struct snd_soc_dai **codec_dais;
 	struct snd_soc_platform *platform;
 	struct device_node *platform_of_node;
+	struct snd_pcm_runtime *runtime;
 	const char *platform_name;
 	int i;
 
@@ -1134,6 +1135,25 @@ static int soc_bind_dai_link(struct snd_soc_card *card,
 	}
 
 	soc_add_pcm_runtime(card, rtd);
+
+	/* if the dai link is virtual, create runtime to set it as running */
+	if (rtd->dai_link->virtual) {
+		runtime = kzalloc(sizeof(*runtime),
+				  GFP_KERNEL);
+		if (!runtime)
+			return -ENOMEM;
+
+		if (rtd->dai_link->dpcm_playback) {
+			rtd->dpcm[SNDRV_PCM_STREAM_PLAYBACK].runtime = runtime;
+			rtd->cpu_dai->playback_active = 1;
+			rtd->codec_dai->playback_active = 1;
+		}
+
+		/* increment the active count for cpu dai */
+		rtd->cpu_dai->active++;
+
+		/* does virtual FE for capture make sense */
+	}
 	return 0;
 
 _err_defer:

sound/soc/soc-dapm.c

@@ -1246,7 +1246,8 @@ int snd_soc_dapm_dai_get_connected_widgets(struct snd_soc_dai *dai, int stream,
 				custom_stop_condition);
 
 	/* Drop starting point */
-	list_del(widgets.next);
+	if (!list_is_singular(&widgets))
+		list_del(widgets.next);
 
 	ret = dapm_widget_list_create(list, &widgets);
 	if (ret)

sound/soc/soc-pcm.c

@@ -1582,7 +1582,6 @@ static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream,
 
 	/* Create any new FE <--> BE connections */
 	for (i = 0; i < list->num_widgets; i++) {
-
 		switch (list->widgets[i]->id) {
 		case snd_soc_dapm_dai_in:
 			if (stream != SNDRV_PCM_STREAM_PLAYBACK)
@@ -2759,6 +2758,8 @@ int soc_dpcm_runtime_update(struct snd_soc_card *card)
 	mutex_unlock(&card->mutex);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(soc_dpcm_runtime_update);
+
 int soc_dpcm_be_digital_mute(struct snd_soc_pcm_runtime *fe, int mute)
 {
 	struct snd_soc_dpcm *dpcm;
@@ -2789,6 +2790,114 @@ int soc_dpcm_be_digital_mute(struct snd_soc_pcm_runtime *fe, int mute)
 	return 0;
 }
 
+/*
+ * create a virtual FE DAI link
+ * Virtual FE DAI links are used in hostless pipelines
+ * to enable the codecs when the pipeline is triggered
+ */
+int soc_dpcm_vfe_new(struct snd_soc_card *card, int index,
+		     const char *link_name, const char *cpu_dai_name,
+		     const char *platform_name)
+{
+	struct snd_soc_dai_link *link;
+
+	link = kzalloc(sizeof(*link), GFP_KERNEL);
+	if (!link)
+		return -ENOMEM;
+
+	dev_dbg(card->dev, "ASoC: adding new virtual FE DAI link %s\n",
+		link_name);
+
+	/* define virtual FE DAI link */
+	link->virtual = 1;
+	link->name = link_name;
+	link->id = 1;
+	link->cpu_dai_name = cpu_dai_name;
+	link->platform_name = platform_name;
+	link->codec_name = "snd-soc-dummy";
+	link->codec_dai_name = "snd-soc-dummy-dai";
+	link->num_codecs = 1;
+
+	/* allocate memory for link codecs */
+	link->codecs = devm_kzalloc(card->dev,
+				    sizeof(struct snd_soc_dai_link_component),
+				    GFP_KERNEL);
+	if (!link->codecs)
+		return -ENOMEM;
+
+	link->codecs[0].name = link->codec_name;
+	link->codecs[0].dai_name = link->codec_dai_name;
+
+	/* enable DPCM */
+	link->dynamic = 1;
+
+	/*TODO: check if we need to handle capture for virtual FE */
+	link->dpcm_playback = 1;
+
+	link->dobj.index = index;
+	link->dobj.type = SND_SOC_DOBJ_DAI_LINK;
+
+	/* add virtual dai link to card dai link list */
+	snd_soc_add_dai_link(card, link);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(soc_dpcm_vfe_new);
+
+/* free virtual FE DAI link */
+int soc_dpcm_vfe_free(struct snd_soc_card *card)
+{
+	struct snd_soc_rtdcom_list *rtdcom1, *rtdcom2;
+	struct snd_soc_pcm_runtime *rtd;
+	struct snd_pcm_str *pstr;
+	int stream_dir;
+
+	list_for_each_entry(rtd, &card->rtd_list, list) {
+
+		/* check if this is a virtual dai link */
+		if (rtd->dai_link->virtual) {
+
+			if (rtd->dai_link->dpcm_playback) {
+				stream_dir = SNDRV_PCM_STREAM_PLAYBACK;
+
+				/* disconnect FE from BE */
+				dpcm_be_disconnect(rtd, stream_dir);
+
+				/* free pcm runtime */
+				kfree(rtd->dpcm[stream_dir].runtime);
+
+				pstr = &rtd->pcm->streams[stream_dir];
+
+				/* free pcm substream amd pcm */
+				kfree(pstr->substream);
+			}
+
+			/* free pcm */
+			kfree(rtd->pcm);
+
+			/* free codec dais and component list */
+			kfree(rtd->codec_dais);
+
+			for_each_rtdcom_safe(rtd, rtdcom1, rtdcom2)
+				kfree(rtdcom1);
+
+			INIT_LIST_HEAD(&rtd->component_list);
+
+			/* remove dai_link from card */
+			snd_soc_remove_dai_link(card, rtd->dai_link);
+
+			/* free link */
+			kfree(rtd->dai_link);
+
+			/* free runtime */
+			kfree(rtd);
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(soc_dpcm_vfe_free);
+
 static int dpcm_fe_dai_open(struct snd_pcm_substream *fe_substream)
 {
 	struct snd_soc_pcm_runtime *fe = fe_substream->private_data;
@@ -3004,7 +3113,9 @@ 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;
@@ -3043,6 +3154,44 @@ 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);