ASoC: dpcm: play nice with CODEC<->CODEC links

Currently in situations where a normal CODEC to CODEC link follows a
DPCM DAI, an error in the following form will be logged:

ASoC: can't get [playback|capture] BE for <widget name>
ASoC: no BE found for <widget name>

This happens because all widgets in a path containing a DPCM DAI will
be passed to dpcm_add_paths, which will try to interpret the CODEC<->CODEC
as if it were a DPCM DAI, in turn causing the error.

This patch aims to resolve the described issue by stopping the DPCM graph
walk, initiated from dpcm_path_get, at the first widget associated with
a DPCM BE.

Signed-off-by: Piotr Stankiewicz <piotrs@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-pcm.c

@@ -1287,6 +1287,46 @@ static int widget_in_list(struct snd_soc_dapm_widget_list *list,
 	return 0;
 }
 
+static bool dpcm_end_walk_at_be(struct snd_soc_dapm_widget *widget,
+		enum snd_soc_dapm_direction dir)
+{
+	struct snd_soc_card *card = widget->dapm->card;
+	struct snd_soc_pcm_runtime *rtd;
+	int i;
+
+	if (dir == SND_SOC_DAPM_DIR_OUT) {
+		list_for_each_entry(rtd, &card->rtd_list, list) {
+			if (!rtd->dai_link->no_pcm)
+				continue;
+
+			if (rtd->cpu_dai->playback_widget == widget)
+				return true;
+
+			for (i = 0; i < rtd->num_codecs; ++i) {
+				struct snd_soc_dai *dai = rtd->codec_dais[i];
+				if (dai->playback_widget == widget)
+					return true;
+			}
+		}
+	} else { /* SND_SOC_DAPM_DIR_IN */
+		list_for_each_entry(rtd, &card->rtd_list, list) {
+			if (!rtd->dai_link->no_pcm)
+				continue;
+
+			if (rtd->cpu_dai->capture_widget == widget)
+				return true;
+
+			for (i = 0; i < rtd->num_codecs; ++i) {
+				struct snd_soc_dai *dai = rtd->codec_dais[i];
+				if (dai->capture_widget == widget)
+					return true;
+			}
+		}
+	}
+
+	return false;
+}
+
 int dpcm_path_get(struct snd_soc_pcm_runtime *fe,
 	int stream, struct snd_soc_dapm_widget_list **list)
 {
@@ -1295,7 +1335,7 @@ int dpcm_path_get(struct snd_soc_pcm_runtime *fe,
 
 	/* get number of valid DAI paths and their widgets */
 	paths = snd_soc_dapm_dai_get_connected_widgets(cpu_dai, stream, list,
-			NULL);
+			dpcm_end_walk_at_be);
 
 	dev_dbg(fe->dev, "ASoC: found %d audio %s paths\n", paths,
 			stream ? "capture" : "playback");