[PATCH v2] ALSA: compress: allow setting codec params after next track

[Srinivas Kandagatla]

For gapless playback it is possible that each track can have different
codec profile with same decoder, for example we have WMA album,
we may have different tracks as WMA v9, WMA v10 and so on

Or if DSP's like QDSP have abililty to switch decoders on single stream
for each track, then this call could be used to set new codec parameters.

Existing code does not allow to change this profile while doing gapless
playback.

Reuse existing SNDRV_COMPRESS_SET_PARAMS to set this new track params along
some additional checks to enforce proper state machine.

With this new changes now the user can call SNDRV_COMPRESS_SET_PARAMS
anytime after setting next track and additional check in write should
also ensure that params are set before writing new data.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
---
Changes since v1/RFC:
	- removed introduction of new IOCTL, as suggested.
	- update the state-machine doc.

 .../sound/designs/compress-offload.rst        | 52 +++++++++----------
 sound/core/compress_offload.c                 | 10 ++--
 2 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/Documentation/sound/designs/compress-offload.rst b/Documentation/sound/designs/compress-offload.rst
index 935f325dbc77..205cadcabe70 100644
--- a/Documentation/sound/designs/compress-offload.rst
+++ b/Documentation/sound/designs/compress-offload.rst
@@ -256,32 +256,32 @@ Gapless Playback SM
 For Gapless, we move from running state to partial drain and back, along
 with setting of meta_data and signalling for next track ::
 
-
-                                        +----------+
-                compr_drain_notify()    |          |
-              +------------------------>|  RUNNING |
-              |                         |          |
-              |                         +----------+
-              |                              |
-              |                              |
-              |                              | compr_next_track()
-              |                              |
-              |                              V
-              |                         +----------+
-              |                         |          |
-              |                         |NEXT_TRACK|
-              |                         |          |
-              |                         +----------+
-              |                              |
-              |                              |
-              |                              | compr_partial_drain()
-              |                              |
-              |                              V
-              |                         +----------+
-              |                         |          |
-              +------------------------ | PARTIAL_ |
-                                        |  DRAIN   |
-                                        +----------+
+                            +----------+
+     compr_drain_notify()   |          | compr_set_params() iff next-track set.
+  +------------------------>|  RUNNING |----------------------+
+  |                         |          |                      |
+  |                         +----------+                      |
+  |                              |                            |
+  |                              |                            |
+  |                              | compr_next_track()         |
+  |                              |                            V
+  |                              V                            |
+  |                         +----------+                      |
+  |                         |          |                      |
+  |                         |NEXT_TRACK|                      |
+  |                         |          |                      |
+  |                         +----------+                      |
+  |                              |                            |
+  |                              +----------------------------+
+  |                              |
+  |                              | compr_partial_drain()
+  |                              |
+  |                              V
+  |                         +----------+
+  |                         |          |
+  +------------------------ | PARTIAL_ |
+                            |  DRAIN   |
+                            +----------+
 
 Not supported
 =============
diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
index 243acad89fd3..fe67228e74b3 100644
--- a/sound/core/compress_offload.c
+++ b/sound/core/compress_offload.c
@@ -294,6 +294,9 @@ static ssize_t snd_compr_write(struct file *f, const char __user *buf,
 	case SNDRV_PCM_STATE_SETUP:
 	case SNDRV_PCM_STATE_PREPARED:
 	case SNDRV_PCM_STATE_RUNNING:
+		/* Make sure next track params are set before writing new data */
+		if (stream->next_track)
+			return -EPERM;
 		break;
 	default:
 		mutex_unlock(&stream->device->lock);
@@ -589,7 +592,8 @@ snd_compr_set_params(struct snd_compr_stream *stream, unsigned long arg)
 	struct snd_compr_params *params;
 	int retval;
 
-	if (stream->runtime->state == SNDRV_PCM_STATE_OPEN) {
+	if (stream->runtime->state == SNDRV_PCM_STATE_OPEN ||
+	    (stream->runtime->state == SNDRV_PCM_STATE_RUNNING && stream->next_track)) {
 		/*
 		 * we should allow parameter change only when stream has been
 		 * opened not in other cases
@@ -615,7 +619,8 @@ snd_compr_set_params(struct snd_compr_stream *stream, unsigned long arg)
 		stream->metadata_set = false;
 		stream->next_track = false;
 
-		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
+		if (stream->runtime->state == SNDRV_PCM_STATE_OPEN)
+			stream->runtime->state = SNDRV_PCM_STATE_SETUP;
 	} else {
 		return -EPERM;
 	}
@@ -956,7 +961,6 @@ static int snd_compr_partial_drain(struct snd_compr_stream *stream)
 		return retval;
 	}
 
-	stream->next_track = false;
 	return snd_compress_wait_for_drain(stream);
 }
 
-- 
2.21.0