[RFC PATCH v3 12/13] ASoC: soc-pcm: test refcount before triggering

[Pierre-Louis Bossart]

On start/pause_release/resume, when more than one FE is connected to
the same BE, it's possible that the trigger is sent more than
once. This is not desirable, we only want to trigger a BE once, which
is straightforward to implement with a refcount.

For stop/pause/suspend, the problem is more complicated: the check
implemented in snd_soc_dpcm_can_be_free_stop() may fail due to a
conceptual deadlock when we trigger the BE before the FE. In this
case, the FE states have not yet changed, so there are corner cases
where the TRIGGER_STOP is never sent - the dual case of start where
multiple triggers might be sent.

This patch suggests an unconditional trigger in all cases, without
checking the FE states, using a refcount protected by the BE PCM
stream lock.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
---
 include/sound/soc-dpcm.h |  2 ++
 sound/soc/soc-pcm.c      | 53 +++++++++++++++++++++++++++++++---------
 2 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/include/sound/soc-dpcm.h b/include/sound/soc-dpcm.h
index 8ed40b8f3da8..9464c588f71d 100644
--- a/include/sound/soc-dpcm.h
+++ b/include/sound/soc-dpcm.h
@@ -101,6 +101,8 @@ struct snd_soc_dpcm_runtime {
 	enum snd_soc_dpcm_state state;
 
 	int trigger_pending; /* trigger cmd + 1 if pending, 0 if not */
+
+	int be_start; /* refcount protected by BE stream pcm lock */
 };
 
 #define for_each_dpcm_fe(be, stream, _dpcm)				\
diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index d115e9409c14..1967980d0f79 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1600,7 +1600,7 @@ int dpcm_be_dai_startup(struct snd_soc_pcm_runtime *fe, int stream)
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_CLOSE;
 			goto unwind;
 		}
-
+		be->dpcm[stream].be_start = 0;
 		be->dpcm[stream].state = SND_SOC_DPCM_STATE_OPEN;
 		count++;
 	}
@@ -2096,14 +2096,21 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 		snd_soc_dpcm_be_lock_irqsave(be, stream, flags);
 		switch (cmd) {
 		case SNDRV_PCM_TRIGGER_START:
-			if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_PREPARE) &&
+			if (!be->dpcm[stream].be_start &&
+			    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_PREPARE) &&
 			    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_STOP) &&
 			    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_PAUSED))
 				goto unlock_be;
 
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
+				goto unlock_be;
+
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start--;
 				goto unlock_be;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
@@ -2111,9 +2118,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_SUSPEND))
 				goto unlock_be;
 
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
+				goto unlock_be;
+
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start--;
 				goto unlock_be;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
@@ -2121,9 +2134,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_PAUSED))
 				goto unlock_be;
 
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
+				goto unlock_be;
+
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start--;
 				goto unlock_be;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
@@ -2132,12 +2151,18 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_PAUSED))
 				goto unlock_be;
 
-			if (!snd_soc_dpcm_can_be_free_stop_locked(fe, be, stream))
+			if (be->dpcm[stream].state == SND_SOC_DPCM_STATE_START)
+				be->dpcm[stream].be_start--;
+
+			if (be->dpcm[stream].be_start != 0)
 				goto unlock_be;
 
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				if (be->dpcm[stream].state == SND_SOC_DPCM_STATE_START)
+					be->dpcm[stream].be_start++;
 				goto unlock_be;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_STOP;
 			break;
@@ -2145,12 +2170,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if (be->dpcm[stream].state != SND_SOC_DPCM_STATE_START)
 				goto unlock_be;
 
-			if (!snd_soc_dpcm_can_be_free_stop_locked(fe, be, stream))
+			be->dpcm[stream].be_start--;
+			if (be->dpcm[stream].be_start != 0)
 				goto unlock_be;
 
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start++;
 				goto unlock_be;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_SUSPEND;
 			break;
@@ -2158,12 +2186,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if (be->dpcm[stream].state != SND_SOC_DPCM_STATE_START)
 				goto unlock_be;
 
-			if (!snd_soc_dpcm_can_be_free_stop_locked(fe, be, stream))
+			be->dpcm[stream].be_start--;
+			if (be->dpcm[stream].be_start != 0)
 				goto unlock_be;
 
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start++;
 				goto unlock_be;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_PAUSED;
 			break;
-- 
2.25.1