ALSA: compress: allow pause and resume during draining

With a stream with low bitrate, user can't pause or resume the stream
near the end of the stream because current ALSA doesn't allow it.
If the stream has very low bitrate enough to store whole stream into
the buffer, user can't do anything except stop the stream and then
restart it from the first because most of applications call draining
after sending last frame to the kernel.
If pause, resume are allowed during draining, user experience can be
enhanced.
To prevent malfunction in HW drivers which don't support pause
during draining, pause during draining will only work if HW driver
enable this feature explicitly by calling
snd_compr_use_pause_in_draining().

Signed-off-by: Gyeongtaek Lee <gt82.lee@samsung.com>
Acked-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/000101d6c3f0$89b312b0$9d193810$@samsung.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/compress_driver.h

@@ -67,6 +67,7 @@ struct snd_compr_runtime {
  * @metadata_set: metadata set flag, true when set
  * @next_track: has userspace signal next track transition, true when set
  * @partial_drain: undergoing partial_drain for stream, true when set
+ * @pause_in_draining: paused during draining state, true when set
  * @private_data: pointer to DSP private data
  * @dma_buffer: allocated buffer if any
  */
@@ -80,6 +81,7 @@ struct snd_compr_stream {
 	bool metadata_set;
 	bool next_track;
 	bool partial_drain;
+	bool pause_in_draining;
 	void *private_data;
 	struct snd_dma_buffer dma_buffer;
 };
@@ -142,6 +144,7 @@ struct snd_compr_ops {
  * @direction: Playback or capture direction
  * @lock: device lock
  * @device: device id
+ * @use_pause_in_draining: allow pause in draining, true when set
  */
 struct snd_compr {
 	const char *name;
@@ -152,6 +155,7 @@ struct snd_compr {
 	unsigned int direction;
 	struct mutex lock;
 	int device;
+	bool use_pause_in_draining;
 #ifdef CONFIG_SND_VERBOSE_PROCFS
 	/* private: */
 	char id[64];
@@ -166,6 +170,18 @@ int snd_compress_deregister(struct snd_compr *device);
 int snd_compress_new(struct snd_card *card, int device,
 			int type, const char *id, struct snd_compr *compr);
 
+/**
+ * snd_compr_use_pause_in_draining - Allow pause and resume in draining state
+ * @substream: compress substream to set
+ *
+ * Allow pause and resume in draining state.
+ * Only HW driver supports this transition can call this API.
+ */
+static inline void snd_compr_use_pause_in_draining(struct snd_compr_stream *substream)
+{
+	substream->device->use_pause_in_draining = true;
+}
+
 /* dsp driver callback apis
  * For playback: driver should call snd_compress_fragment_elapsed() to let the
  * framework know that a fragment has been consumed from the ring buffer

sound/core/compress_offload.c

@@ -709,11 +709,22 @@ static int snd_compr_pause(struct snd_compr_stream *stream)
 {
 	int retval;
 
-	if (stream->runtime->state != SNDRV_PCM_STATE_RUNNING)
+	switch (stream->runtime->state) {
-		return -EPERM;
+	case SNDRV_PCM_STATE_RUNNING:
 		retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_PUSH);
 		if (!retval)
 			stream->runtime->state = SNDRV_PCM_STATE_PAUSED;
+		break;
+	case SNDRV_PCM_STATE_DRAINING:
+		if (!stream->device->use_pause_in_draining)
+			return -EPERM;
+		retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_PUSH);
+		if (!retval)
+			stream->pause_in_draining = true;
+		break;
+	default:
+		return -EPERM;
+	}
 	return retval;
 }
 
@@ -721,11 +732,22 @@ static int snd_compr_resume(struct snd_compr_stream *stream)
 {
 	int retval;
 
-	if (stream->runtime->state != SNDRV_PCM_STATE_PAUSED)
+	switch (stream->runtime->state) {
-		return -EPERM;
+	case SNDRV_PCM_STATE_PAUSED:
 		retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_RELEASE);
 		if (!retval)
 			stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
+		break;
+	case SNDRV_PCM_STATE_DRAINING:
+		if (!stream->pause_in_draining)
+			return -EPERM;
+		retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_RELEASE);
+		if (!retval)
+			stream->pause_in_draining = false;
+		break;
+	default:
+		return -EPERM;
+	}
 	return retval;
 }
 
@@ -768,6 +790,7 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
 		/* clear flags and stop any drain wait */
 		stream->partial_drain = false;
 		stream->metadata_set = false;
+		stream->pause_in_draining = false;
 		snd_compr_drain_notify(stream);
 		stream->runtime->total_bytes_available = 0;
 		stream->runtime->total_bytes_transferred = 0;