[PATCH v2] ASoC: dpcm: improve runtime update predictability

[Jerome Brunet]

As it is, dpcm_runtime_update() performs the old path and new path
update of a frontend before going on to the next frontend DAI.
Depending the order of the FEs within the rtd list, the result of
the update might be different.

For example:
 * Frontend A connected to backend C, with a 48kHz playback
 * Frontend B connected to backend D, with a 44.1kHz playback
 * FE A appears before FE B in the rtd list of the card.

If we reparent BE C to FE B (disconnecting BE D):
* old path update of FE A will run first, and BE C will get hw_free()
  and shutdown()
* new path update of FE B will run after and BE C, which is stopped,
  so it will be configured at 44.1kHz, as expected

If we reparent BE D to FE A (disconnecting BE C):
* new path update of FE A will run first but since BE D is still running
  at 44.1kHz, it won't be reconfigured (no call to startup() or
  hw_params())
* old path update of FE B runs after, nothing happens
* In this case, we end up with a BE playing at 44.1kHz a stream which is
  supposed to be played at 48Khz (too slow)

To improve this situation, this patch performs all the FE old paths update
before going on to update the new paths. With this, the result should
no longer depend on the order of the FE within the card rtd list.

Please note that there might be a small performance penalty since
dpcm_process_paths() is called twice per stream direction.

Signed-off-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
---

Changes since v1 [0]:
 * Add missing static as reported by kbuild robot.

[0]: https://lkml.kernel.org/r/20180625082923.25636-1-jbrunet@xxxxxxxxxxxx

 sound/soc/soc-pcm.c | 165 +++++++++++++++++++++++++++-------------------------
 1 file changed, 86 insertions(+), 79 deletions(-)

diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index 5e7ae47a9658..4eda18cfe895 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -2543,106 +2543,113 @@ static int dpcm_run_old_update(struct snd_soc_pcm_runtime *fe, int stream)
 	return ret;
 }
 
-/* Called by DAPM mixer/mux changes to update audio routing between PCMs and
- * any DAI links.
- */
-int soc_dpcm_runtime_update(struct snd_soc_card *card)
+static int soc_dpcm_fe_runtime_update(struct snd_soc_pcm_runtime *fe, int new)
 {
-	struct snd_soc_pcm_runtime *fe;
-	int old, new, paths;
+	struct snd_soc_dapm_widget_list *list;
+	int count, paths;
 
-	mutex_lock_nested(&card->mutex, SND_SOC_CARD_CLASS_RUNTIME);
-	list_for_each_entry(fe, &card->rtd_list, list) {
-		struct snd_soc_dapm_widget_list *list;
+	if (!fe->dai_link->dynamic)
+		return 0;
 
-		/* make sure link is FE */
-		if (!fe->dai_link->dynamic)
-			continue;
+	/* only check active links */
+	if (!fe->cpu_dai->active)
+		return 0;
 
-		/* only check active links */
-		if (!fe->cpu_dai->active)
-			continue;
+	/* DAPM sync will call this to update DSP paths */
+	dev_dbg(fe->dev, "ASoC: DPCM %s runtime update for FE %s\n",
+		new ? "new" : "old", fe->dai_link->name);
 
-		/* DAPM sync will call this to update DSP paths */
-		dev_dbg(fe->dev, "ASoC: DPCM runtime update for FE %s\n",
-			fe->dai_link->name);
+	/* skip if FE doesn't have playback capability */
+	if (!fe->cpu_dai->driver->playback.channels_min ||
+	    !fe->codec_dai->driver->playback.channels_min)
+		goto capture;
 
-		/* skip if FE doesn't have playback capability */
-		if (!fe->cpu_dai->driver->playback.channels_min
-		    || !fe->codec_dai->driver->playback.channels_min)
-			goto capture;
-
-		/* skip if FE isn't currently playing */
-		if (!fe->cpu_dai->playback_active
-		    || !fe->codec_dai->playback_active)
-			goto capture;
-
-		paths = dpcm_path_get(fe, SNDRV_PCM_STREAM_PLAYBACK, &list);
-		if (paths < 0) {
-			dev_warn(fe->dev, "ASoC: %s no valid %s path\n",
-					fe->dai_link->name,  "playback");
-			mutex_unlock(&card->mutex);
-			return paths;
-		}
+	/* skip if FE isn't currently playing */
+	if (!fe->cpu_dai->playback_active || !fe->codec_dai->playback_active)
+		goto capture;
 
-		/* update any new playback paths */
-		new = dpcm_process_paths(fe, SNDRV_PCM_STREAM_PLAYBACK, &list, 1);
-		if (new) {
-			dpcm_run_new_update(fe, SNDRV_PCM_STREAM_PLAYBACK);
-			dpcm_clear_pending_state(fe, SNDRV_PCM_STREAM_PLAYBACK);
-			dpcm_be_disconnect(fe, SNDRV_PCM_STREAM_PLAYBACK);
-		}
+	paths = dpcm_path_get(fe, SNDRV_PCM_STREAM_PLAYBACK, &list);
+	if (paths < 0) {
+		dev_warn(fe->dev, "ASoC: %s no valid %s path\n",
+			 fe->dai_link->name,  "playback");
+		return paths;
+	}
 
-		/* update any old playback paths */
-		old = dpcm_process_paths(fe, SNDRV_PCM_STREAM_PLAYBACK, &list, 0);
-		if (old) {
+	/* update any playback paths */
+	count = dpcm_process_paths(fe, SNDRV_PCM_STREAM_PLAYBACK, &list, new);
+	if (count) {
+		if (new)
+			dpcm_run_new_update(fe, SNDRV_PCM_STREAM_PLAYBACK);
+		else
 			dpcm_run_old_update(fe, SNDRV_PCM_STREAM_PLAYBACK);
-			dpcm_clear_pending_state(fe, SNDRV_PCM_STREAM_PLAYBACK);
-			dpcm_be_disconnect(fe, SNDRV_PCM_STREAM_PLAYBACK);
-		}
 
-		dpcm_path_put(&list);
+		dpcm_clear_pending_state(fe, SNDRV_PCM_STREAM_PLAYBACK);
+		dpcm_be_disconnect(fe, SNDRV_PCM_STREAM_PLAYBACK);
+	}
+
+	dpcm_path_put(&list);
+
 capture:
-		/* skip if FE doesn't have capture capability */
-		if (!fe->cpu_dai->driver->capture.channels_min
-		    || !fe->codec_dai->driver->capture.channels_min)
-			continue;
+	/* skip if FE doesn't have capture capability */
+	if (!fe->cpu_dai->driver->capture.channels_min ||
+	    !fe->codec_dai->driver->capture.channels_min)
+		return 0;
 
-		/* skip if FE isn't currently capturing */
-		if (!fe->cpu_dai->capture_active
-		    || !fe->codec_dai->capture_active)
-			continue;
+	/* skip if FE isn't currently capturing */
+	if (!fe->cpu_dai->capture_active || !fe->codec_dai->capture_active)
+		return 0;
 
-		paths = dpcm_path_get(fe, SNDRV_PCM_STREAM_CAPTURE, &list);
-		if (paths < 0) {
-			dev_warn(fe->dev, "ASoC: %s no valid %s path\n",
-					fe->dai_link->name,  "capture");
-			mutex_unlock(&card->mutex);
-			return paths;
-		}
+	paths = dpcm_path_get(fe, SNDRV_PCM_STREAM_CAPTURE, &list);
+	if (paths < 0) {
+		dev_warn(fe->dev, "ASoC: %s no valid %s path\n",
+			 fe->dai_link->name,  "capture");
+		return paths;
+	}
 
-		/* update any new capture paths */
-		new = dpcm_process_paths(fe, SNDRV_PCM_STREAM_CAPTURE, &list, 1);
-		if (new) {
+	/* update any old capture paths */
+	count = dpcm_process_paths(fe, SNDRV_PCM_STREAM_CAPTURE, &list, new);
+	if (count) {
+		if (new)
 			dpcm_run_new_update(fe, SNDRV_PCM_STREAM_CAPTURE);
-			dpcm_clear_pending_state(fe, SNDRV_PCM_STREAM_CAPTURE);
-			dpcm_be_disconnect(fe, SNDRV_PCM_STREAM_CAPTURE);
-		}
-
-		/* update any old capture paths */
-		old = dpcm_process_paths(fe, SNDRV_PCM_STREAM_CAPTURE, &list, 0);
-		if (old) {
+		else
 			dpcm_run_old_update(fe, SNDRV_PCM_STREAM_CAPTURE);
-			dpcm_clear_pending_state(fe, SNDRV_PCM_STREAM_CAPTURE);
-			dpcm_be_disconnect(fe, SNDRV_PCM_STREAM_CAPTURE);
-		}
 
-		dpcm_path_put(&list);
+		dpcm_clear_pending_state(fe, SNDRV_PCM_STREAM_CAPTURE);
+		dpcm_be_disconnect(fe, SNDRV_PCM_STREAM_CAPTURE);
 	}
 
-	mutex_unlock(&card->mutex);
+	dpcm_path_put(&list);
+
 	return 0;
 }
+
+/* Called by DAPM mixer/mux changes to update audio routing between PCMs and
+ * any DAI links.
+ */
+int soc_dpcm_runtime_update(struct snd_soc_card *card)
+{
+	struct snd_soc_pcm_runtime *fe;
+	int ret = 0;
+
+	mutex_lock_nested(&card->mutex, SND_SOC_CARD_CLASS_RUNTIME);
+	/* shutdown all old paths first */
+	list_for_each_entry(fe, &card->rtd_list, list) {
+		ret = soc_dpcm_fe_runtime_update(fe, 0);
+		if (ret)
+			goto out;
+	}
+
+	/* bring new paths up */
+	list_for_each_entry(fe, &card->rtd_list, list) {
+		ret = soc_dpcm_fe_runtime_update(fe, 1);
+		if (ret)
+			goto out;
+	}
+
+out:
+	mutex_unlock(&card->mutex);
+	return ret;
+}
 int soc_dpcm_be_digital_mute(struct snd_soc_pcm_runtime *fe, int mute)
 {
 	struct snd_soc_dpcm *dpcm;
-- 
2.14.4