[PATCH v2] ASoC: Handle multiple codecs with split playback / capture

[Ricard Wanderlof <ricard.wanderlof@axis.com>]

Add the capability to use multiple codecs on the same DAI linke where
one codec is used for playback and another one is used for capture.

Tested on a setup using an SSM2518 for playback and an ICS43432 I2S MEMS
microphone for capture.

Signed-off-by: Ricard Wanderlof <ricardw@axis.com>
---

The patch was created after a discussion on the alsa-devel mailing list
as to how best to implement this functionality.
(http://mailman.alsa-project.org/pipermail/alsa-devel/2015-June/093214.html).

V2: Minor code change, otherwise the differences compared to V1 are solely
related to comments, in particular considerations given to the 
potential consequences of the patch. After consideration, it seems to me 
that the patch as it stands augments the current framework with the 
functionality indicated in the commit message above, without restricting 
other current uses. Further functionality could be added, but IMHO that 
should be done as the need arises, when it can be properly tested in a 
real-world setup.

 sound/soc/soc-pcm.c |   49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index 35fe58f4..08407ba 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -34,6 +34,24 @@
 
 #define DPCM_MAX_BE_USERS	8
 
+/*
+ * snd_soc_dai_stream_valid() - check if a DAI supports the given stream
+ *
+ * Returns true if the DAI supports the indicated stream type.
+ */
+static bool snd_soc_dai_stream_valid(struct snd_soc_dai *dai, int stream)
+{
+	struct snd_soc_pcm_stream *codec_stream;
+
+	if (stream == SNDRV_PCM_STREAM_PLAYBACK)
+		codec_stream = &dai->driver->playback;
+	else
+		codec_stream = &dai->driver->capture;
+
+	/* If the codec specifies any rate at all, it supports the stream. */
+	return codec_stream->rates;
+}
+
 /**
  * snd_soc_runtime_activate() - Increment active count for PCM runtime components
  * @rtd: ASoC PCM runtime that is activated
@@ -371,6 +389,20 @@ static void soc_pcm_init_runtime_hw(struct snd_pcm_substream *substream)
 
 	/* first calculate min/max only for CODECs in the DAI link */
 	for (i = 0; i < rtd->num_codecs; i++) {
+
+		/*
+		 * Skip CODECs which don't support the current stream type.
+		 * Otherwise, since the rate, channel, and format values will
+		 * zero in that case, we would have no usable settings left,
+		 * causing the resulting setup to fail.
+		 * At least one CODEC should match, otherwise we should have
+		 * bailed out on a higher level, since there would be no
+		 * CODEC to support the transfer direction in that case.
+		 */
+		if (!snd_soc_dai_stream_valid(rtd->codec_dais[i],
+					      substream->stream))
+			continue;
+
 		codec_dai_drv = rtd->codec_dais[i]->driver;
 		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
 			codec_stream = &codec_dai_drv->playback;
@@ -827,6 +859,23 @@ static int soc_pcm_hw_params(struct snd_pcm_substream *substream,
 		struct snd_soc_dai *codec_dai = rtd->codec_dais[i];
 		struct snd_pcm_hw_params codec_params;
 
+		/*
+		 * Skip CODECs which don't support the current stream type,
+		 * the idea being that if a CODEC is not used for the currently
+		 * set up transfer direction, it should not need to be
+		 * configured, especially since the configuration used might
+		 * not even be supported by that CODEC. There may be cases
+		 * however where a CODEC needs to be set up although it is
+		 * actually not being used for the transfer, e.g. if a
+		 * capture-only CODEC is acting as an LRCLK and/or BCLK master
+		 * for the DAI link including a playback-only CODEC.
+		 * If this becomes necessary, we will have to augment the
+		 * machine driver setup with information on how to act, so
+		 * we can do the right thing here.
+		 */
+		if (!snd_soc_dai_stream_valid(codec_dai, substream->stream))
+			continue;
+
 		/* copy params for each codec */
 		codec_params = *params;
 
-- 
1.7.10.4


-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30