pcm: hw: introduce SNDRV_PCM_INFO_PERFECT_DRAIN

Handle the driver informing us that it is not necessary to set up
silencing upon playback draining. This will be the case for drivers
which are guaranteed to not read any samples beyond the application
pointer.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

5 files changed, 30 insertions, 1 deletions

diff --git a/include/pcm.h b/include/pcm.h
index b5a514fa..dd031b6c 100644
--- a/include/pcm.h
+++ b/include/pcm.h
@@ -722,6 +722,7 @@ int snd_pcm_hw_params_is_half_duplex(const snd_pcm_hw_params_t *params);
 int snd_pcm_hw_params_is_joint_duplex(const snd_pcm_hw_params_t *params);
 int snd_pcm_hw_params_can_sync_start(const snd_pcm_hw_params_t *params);
 int snd_pcm_hw_params_can_disable_period_wakeup(const snd_pcm_hw_params_t *params);
+int snd_pcm_hw_params_is_perfect_drain(const snd_pcm_hw_params_t *params);
 int snd_pcm_hw_params_supports_audio_wallclock_ts(const snd_pcm_hw_params_t *params); /* deprecated, use audio_ts_type */
 int snd_pcm_hw_params_supports_audio_ts_type(const snd_pcm_hw_params_t *params, int type);
 int snd_pcm_hw_params_get_rate_numden(const snd_pcm_hw_params_t *params,
diff --git a/include/sound/uapi/asound.h b/include/sound/uapi/asound.h
index fc18c024..0b8834f2 100644
--- a/include/sound/uapi/asound.h
+++ b/include/sound/uapi/asound.h
@@ -281,6 +281,7 @@ typedef int __bitwise snd_pcm_subformat_t;
 #define SNDRV_PCM_INFO_DOUBLE		0x00000004	/* Double buffering needed for PCM start/stop */
 #define SNDRV_PCM_INFO_BATCH		0x00000010	/* double buffering */
 #define SNDRV_PCM_INFO_SYNC_APPLPTR	0x00000020	/* need the explicit sync of appl_ptr update */
+#define SNDRV_PCM_INFO_PERFECT_DRAIN	0x00000040	/* silencing at the end of stream is not required */
 #define SNDRV_PCM_INFO_INTERLEAVED	0x00000100	/* channels are interleaved */
 #define SNDRV_PCM_INFO_NONINTERLEAVED	0x00000200	/* channels are not interleaved */
 #define SNDRV_PCM_INFO_COMPLEX		0x00000400	/* complex frame organization (mmap only) */
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
index 88b13ed4..d387da3d 100644
--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -3708,6 +3708,29 @@ int snd_pcm_hw_params_can_disable_period_wakeup(const snd_pcm_hw_params_t *param
 }
 
 /**
+ * \brief Check if hardware is capable of perfect drain
+ * \param params Configuration space
+ * \retval 0 Hardware doesn't do perfect drain
+ * \retval 1 Hardware does perfect drain
+ *
+ * This function should only be called when the configuration space
+ * contains a single configuration. Call #snd_pcm_hw_params to choose
+ * a single configuration from the configuration space.
+ *
+ * Perfect drain means that the hardware does not use samples
+ * beyond the stream application pointer.
+ */
+int snd_pcm_hw_params_is_perfect_drain(const snd_pcm_hw_params_t *params)
+{
+	assert(params);
+	if (CHECK_SANITY(params->info == ~0U)) {
+		SNDMSG("invalid PCM info field");
+		return 0; /* FIXME: should be a negative error? */
+	}
+	return !!(params->info & SNDRV_PCM_INFO_PERFECT_DRAIN);
+}
+
+/**
  * \brief Check if hardware supports audio wallclock timestamps
  * \param params Configuration space
  * \retval 0 Hardware doesn't support audio wallclock timestamps
diff --git a/src/pcm/pcm_hw.c b/src/pcm/pcm_hw.c
index 6d7b2d48..37a18b86 100644
--- a/src/pcm/pcm_hw.c
+++ b/src/pcm/pcm_hw.c
@@ -99,6 +99,7 @@ typedef struct {
 	struct snd_pcm_sync_ptr *sync_ptr;
 
 	bool prepare_reset_sw_params;
+	bool perfect_drain;
 
 	int period_event;
 	snd_timer_t *period_timer;
@@ -398,6 +399,7 @@ static int snd_pcm_hw_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params)
 	params->info &= ~0xf0000000;
 	if (pcm->tstamp_type != SND_PCM_TSTAMP_TYPE_GETTIMEOFDAY)
 		params->info |= SND_PCM_INFO_MONOTONIC;
+	hw->perfect_drain = !!(params->info & SND_PCM_INFO_PERFECT_DRAIN);
 	return query_status_data(hw);
 }
 
@@ -739,7 +741,7 @@ static int snd_pcm_hw_drain(snd_pcm_t *pcm)
 
 	if (pcm->stream != SND_PCM_STREAM_PLAYBACK)
 		goto __skip_silence;
-	if (hw->drain_silence == 0)
+	if (hw->drain_silence == 0 || hw->perfect_drain)
 		goto __skip_silence;
 	snd_pcm_sw_params_current_no_lock(pcm, &sw_params);
 	if (hw->drain_silence > 0) {
diff --git a/src/pcm/pcm_local.h b/src/pcm/pcm_local.h
index 4a859cd1..b039dda0 100644
--- a/src/pcm/pcm_local.h
+++ b/src/pcm/pcm_local.h
@@ -79,6 +79,8 @@
 #define SND_PCM_INFO_DOUBLE SNDRV_PCM_INFO_DOUBLE
 /** device transfers samples in batch */
 #define SND_PCM_INFO_BATCH SNDRV_PCM_INFO_BATCH
+/** device does perfect drain (silencing not required) */
+#define SND_PCM_INFO_PERFECT_DRAIN SNDRV_PCM_INFO_PERFECT_DRAIN
 /** device accepts interleaved samples */
 #define SND_PCM_INFO_INTERLEAVED SNDRV_PCM_INFO_INTERLEAVED
 /** device accepts non-interleaved samples */