ASoC: soc-pcm: test refcount before triggering

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 <[e-mail]>
Reviewed-by: Kai Vehmanen <[e-mail]>
Reviewed-by: Bard Liao <[e-mail]>
Reviewed-by: Ranjani Sridharan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

include/sound/soc-dpcm.h

···
 	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)				\

sound/soc/soc-pcm.c

···
 			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++;
 	}
···
 
 		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;
 
-			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
 				goto next;
+
+			ret = soc_pcm_trigger(be_substream, cmd);
+			if (ret) {
+				be->dpcm[stream].be_start--;
+				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
···
 			if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_SUSPEND))
 				goto next;
 
-			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
 				goto next;
+
+			ret = soc_pcm_trigger(be_substream, cmd);
+			if (ret) {
+				be->dpcm[stream].be_start--;
+				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
···
 			if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_PAUSED))
 				goto next;
 
-			ret = soc_pcm_trigger(be_substream, cmd);
-			if (ret)
+			be->dpcm[stream].be_start++;
+			if (be->dpcm[stream].be_start != 1)
 				goto next;
+
+			ret = soc_pcm_trigger(be_substream, cmd);
+			if (ret) {
+				be->dpcm[stream].be_start--;
+				goto next;
+			}
 
 			be->dpcm[stream].state = SND_SOC_DPCM_STATE_START;
 			break;
···
 			    (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;
···
 			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;
···
 			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;