[PATCH 5/6] ASoC: soc-pcm: test refcount before triggering

[yixuanjiang]

From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>

[ Upstream commit 848aedfdc6ba25ad5652797db9266007773e44dd ]

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>
Reviewed-by: Kai Vehmanen <kai.vehmanen@xxxxxxxxxxxxxxx>
Reviewed-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20211207173745.15850-6-pierre-louis.bossart@xxxxxxxxxxxxxxx
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Fixes: aa9ff6a4955f ("ASoC: soc-compress: Reposition and add pcm_mutex")
Signed-off-by: Yixuan Jiang <yixuanjiang@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 5.15+
---
 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 e296a3949b18b..d963f3b608489 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 7903516c89a6a..b6099d36518f5 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1630,7 +1630,7 @@ 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++;
 	}
@@ -2116,14 +2116,21 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 
 		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 next;
 
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
+				goto next;
+
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start--;
 				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
@@ -2131,9 +2138,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_SUSPEND))
 				goto next;
 
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
+				goto next;
+
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start--;
 				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
@@ -2141,9 +2154,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_PAUSED))
 				goto next;
 
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
+				goto next;
+
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start--;
 				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
@@ -2152,12 +2171,18 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_PAUSED))
 				goto next;
 
-			if (!snd_soc_dpcm_can_be_free_stop(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 next;
 
 			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 next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_STOP;
 			break;
@@ -2165,12 +2190,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if (be->dpcm[stream].state != SND_SOC_DPCM_STATE_START)
 				goto next;
 
-			if (!snd_soc_dpcm_can_be_free_stop(fe, be, stream))
+			be->dpcm[stream].be_start--;
+			if (be->dpcm[stream].be_start != 0)
 				goto next;
 
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start++;
 				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_SUSPEND;
 			break;
@@ -2178,12 +2206,15 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			if (be->dpcm[stream].state != SND_SOC_DPCM_STATE_START)
 				goto next;
 
-			if (!snd_soc_dpcm_can_be_free_stop(fe, be, stream))
+			be->dpcm[stream].be_start--;
+			if (be->dpcm[stream].be_start != 0)
 				goto next;
 
 			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			if (ret) {
+				be->dpcm[stream].be_start++;
 				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_PAUSED;
 			break;
-- 
2.40.1.521.gf1e218fcd8-goog