[PATCH alsa-lib 3/4] pcm: hw: introduce SNDRV_PCM_INFO_PERFECT_DRAIN

[Jaroslav Kysela <perex@perex.cz>]

The driver may not require to touch the sample stream
for the drain operation at all. Handle this situation
in alsa-lib.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
---
 include/pcm.h               |  1 +
 include/sound/uapi/asound.h |  1 +
 src/pcm/pcm.c               | 23 +++++++++++++++++++++++
 src/pcm/pcm_hw.c            |  4 +++-
 src/pcm/pcm_local.h         |  2 ++
 5 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/include/pcm.h b/include/pcm.h
index b5a514fa..f15462d9 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_does_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..099d83ee 100644
--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -3707,6 +3707,29 @@ int snd_pcm_hw_params_can_disable_period_wakeup(const snd_pcm_hw_params_t *param
 	return !!(params->info & SNDRV_PCM_INFO_NO_PERIOD_WAKEUP);
 }
 
+/**
+ * \brief Check if hardware does 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.
+ *
+ * The perfect drain means that the hardware does not use samples
+ * beyond the stream application pointer.
+ */
+int snd_pcm_hw_params_does_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
diff --git a/src/pcm/pcm_hw.c b/src/pcm/pcm_hw.c
index 30ff843c..ea0c2ef2 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 */
-- 
2.39.2