[alsa-devel] [PATCH 4/4] ASoC: simple-card: Add support for codec-to-codec dai_links

[Samuel Holland]

For now we assume there are only a few sets of valid PCM stream
parameters, to avoid needing to specify them in the device tree. We
also assume they are the same in both directions. We calculate the
common subset of parameters, and then the existing code automatically
chooses the highest quality of the remaining values.

Signed-off-by: Samuel Holland <samuel at sholland.org>
---
 .../devicetree/bindings/sound/simple-card.txt |  1 +
 Documentation/sound/soc/codec-to-codec.rst    |  9 ++++-
 include/sound/simple_card_utils.h             |  1 +
 sound/soc/generic/simple-card-utils.c         | 39 +++++++++++++++++++
 sound/soc/generic/simple-card.c               | 12 ++++++
 5 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/sound/simple-card.txt b/Documentation/devicetree/bindings/sound/simple-card.txt
index 79954cd6e37b..18a62e404a30 100644
--- a/Documentation/devicetree/bindings/sound/simple-card.txt
+++ b/Documentation/devicetree/bindings/sound/simple-card.txt
@@ -63,6 +63,7 @@ Optional dai-link subnode properties:
 - mclk-fs             			: Multiplication factor between stream
 					  rate and codec mclk, applied only for
 					  the dai-link.
+- codec-to-codec			: Indicates a codec-to-codec dai-link.
 
 For backward compatibility the frame-master and bitclock-master
 properties can be used as booleans in codec subnode to indicate if the
diff --git a/Documentation/sound/soc/codec-to-codec.rst b/Documentation/sound/soc/codec-to-codec.rst
index 810109d7500d..efe0a8c07933 100644
--- a/Documentation/sound/soc/codec-to-codec.rst
+++ b/Documentation/sound/soc/codec-to-codec.rst
@@ -104,5 +104,10 @@ Make sure to name your corresponding cpu and codec playback and capture
 dai names ending with "Playback" and "Capture" respectively as dapm core
 will link and power those dais based on the name.
 
-Note that in current device tree there is no way to mark a dai_link
-as codec to codec. However, it may change in future.
+A dai_link in a "simple-audio-card" can be marked as codec to codec in
+the device tree by adding the "codec-to-codec" property. The dai_link
+will be initialized with the subset of stream parameters (channels,
+format, sample rate) supported by all DAIs on the link. Since there is
+no way to provide these parameters in the device tree, this is mostly
+useful for communication with simple fixed-function codecs, such as a
+Bluetooth controller or cellular modem.
diff --git a/include/sound/simple_card_utils.h b/include/sound/simple_card_utils.h
index bbdd1542d6f1..80b60237b3cd 100644
--- a/include/sound/simple_card_utils.h
+++ b/include/sound/simple_card_utils.h
@@ -49,6 +49,7 @@ struct asoc_simple_priv {
 		struct asoc_simple_data adata;
 		struct snd_soc_codec_conf *codec_conf;
 		unsigned int mclk_fs;
+		bool codec_to_codec;
 	} *dai_props;
 	struct asoc_simple_jack hp_jack;
 	struct asoc_simple_jack mic_jack;
diff --git a/sound/soc/generic/simple-card-utils.c b/sound/soc/generic/simple-card-utils.c
index 9b794775df53..2de4cfead790 100644
--- a/sound/soc/generic/simple-card-utils.c
+++ b/sound/soc/generic/simple-card-utils.c
@@ -331,6 +331,41 @@ static int asoc_simple_init_dai(struct snd_soc_dai *dai,
 	return 0;
 }
 
+static int asoc_simple_init_dai_link_params(struct snd_soc_pcm_runtime *rtd,
+					    struct simple_dai_props *dai_props)
+{
+	struct snd_soc_dai_link *dai_link = rtd->dai_link;
+	struct snd_soc_pcm_stream *params;
+	struct snd_pcm_hardware hw;
+	int ret;
+
+	if (!dai_props->codec_to_codec)
+		return 0;
+
+	/* Assumes the hardware capabilities are the same in both directions */
+	ret = snd_soc_runtime_calc_hw(rtd, &hw, SNDRV_PCM_STREAM_PLAYBACK);
+	if (ret < 0) {
+		dev_err(rtd->dev, "simple-card: no valid dai_link params\n");
+		return ret;
+	}
+
+	params = devm_kzalloc(rtd->dev, sizeof(*params), GFP_KERNEL);
+	if (!params)
+		return -ENOMEM;
+
+	params->formats = hw.formats;
+	params->rates = hw.rates;
+	params->rate_min = hw.rate_min;
+	params->rate_max = hw.rate_max;
+	params->channels_min = hw.channels_min;
+	params->channels_max = hw.channels_max;
+
+	dai_link->params = params;
+	dai_link->num_params = 1;
+
+	return 0;
+}
+
 int asoc_simple_dai_init(struct snd_soc_pcm_runtime *rtd)
 {
 	struct asoc_simple_priv *priv = snd_soc_card_get_drvdata(rtd->card);
@@ -347,6 +382,10 @@ int asoc_simple_dai_init(struct snd_soc_pcm_runtime *rtd)
 	if (ret < 0)
 		return ret;
 
+	ret = asoc_simple_init_dai_link_params(rtd, dai_props);
+	if (ret < 0)
+		return ret;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(asoc_simple_dai_init);
diff --git a/sound/soc/generic/simple-card.c b/sound/soc/generic/simple-card.c
index 55e9f8800b3e..179ab4482d10 100644
--- a/sound/soc/generic/simple-card.c
+++ b/sound/soc/generic/simple-card.c
@@ -77,6 +77,16 @@ static int asoc_simple_parse_dai(struct device_node *node,
 	return 0;
 }
 
+static void simple_parse_codec_to_codec(struct device_node *node,
+					struct simple_dai_props *props,
+					char *prefix)
+{
+	char prop[128];
+
+	snprintf(prop, sizeof(prop), "%scodec-to-codec", prefix);
+	props->codec_to_codec = of_property_read_bool(node, prop);
+}
+
 static void simple_parse_convert(struct device *dev,
 				 struct device_node *np,
 				 struct asoc_simple_data *adata)
@@ -217,6 +227,7 @@ static int simple_dai_link_of_dpcm(struct asoc_simple_priv *priv,
 					     "prefix");
 	}
 
+	simple_parse_codec_to_codec(node, dai_props, prefix);
 	simple_parse_convert(dev, np, &dai_props->adata);
 	simple_parse_mclk_fs(top, np, codec, dai_props, prefix);
 
@@ -292,6 +303,7 @@ static int simple_dai_link_of(struct asoc_simple_priv *priv,
 	if (ret < 0)
 		goto dai_link_of_err;
 
+	simple_parse_codec_to_codec(node, dai_props, prefix);
 	simple_parse_mclk_fs(top, cpu, codec, dai_props, prefix);
 
 	ret = asoc_simple_parse_cpu(cpu, dai_link, &single_cpu);
-- 
2.24.1