ASoC: make snd_soc_dai_link more symmetrical

Prior to this patch, the CPU side of a DAI link was specified using a
single name. Often, this was the result of calling dev_name() on the
device providing the DAI, but in the case of a CPU DAI driver that
provided multiple DAIs, it needed to mix together both the device name
and some device-relative name, in order to form a single globally unique
name.

However, the CODEC side of the DAI link was specified using separate
fields for device (name or OF node) and device-relative DAI name.

This patch allows the CPU side of a DAI link to be specified in the same
way as the CODEC side, separating concepts of device and device-relative
DAI name.

I believe this will be important in multi-codec and/or dynamic PCM
scenarios, where a single CPU driver provides multiple DAIs, while also
booting using device tree, with accompanying desire not to hard-code the
CPU side device's name into the original .cpu_dai_name field.

Ideally, both the CPU DAI and CODEC DAI loops in soc_bind_dai_link()
would now be identical. However, two things prevent that at present:

1) The need to save rtd->codec for the CODEC side, which means we have
to search for the CODEC explicitly, and not just the CODEC side DAI.

2) Since we know the CODEC side DAI is part of a codec, and not just
a standalone DAI, it's slightly more efficient to convert .codec_name/
.codec_of_node into a codec first, and then compare each DAI's .codec
field, since this avoids strcmp() on each DAI's CODEC's name within
the loop.

However, the two loops are essentially semantically equivalent.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

1 files changed, 28 insertions, 5 deletions

diff --git a/include/sound/soc.h b/include/sound/soc.h
index c703871f5f65..23c4efbe13a6 100644
--- a/include/sound/soc.h
+++ b/include/sound/soc.h
@@ -785,13 +785,36 @@ struct snd_soc_dai_link {
 	/* config - must be set by machine driver */
 	const char *name;			/* Codec name */
 	const char *stream_name;		/* Stream name */
-	const char *codec_name;		/* for multi-codec */
-	const struct device_node *codec_of_node;
-	const char *platform_name;	/* for multi-platform */
-	const struct device_node *platform_of_node;
+	/*
+	 * You MAY specify the link's CPU-side device, either by device name,
+	 * or by DT/OF node, but not both. If this information is omitted,
+	 * the CPU-side DAI is matched using .cpu_dai_name only, which hence
+	 * must be globally unique. These fields are currently typically used
+	 * only for codec to codec links, or systems using device tree.
+	 */
+	const char *cpu_name;
+	const struct device_node *cpu_of_node;
+	/*
+	 * You MAY specify the DAI name of the CPU DAI. If this information is
+	 * omitted, the CPU-side DAI is matched using .cpu_name/.cpu_of_node
+	 * only, which only works well when that device exposes a single DAI.
+	 */
 	const char *cpu_dai_name;
-	const struct device_node *cpu_dai_of_node;
+	/*
+	 * You MUST specify the link's codec, either by device name, or by
+	 * DT/OF node, but not both.
+	 */
+	const char *codec_name;
+	const struct device_node *codec_of_node;
+	/* You MUST specify the DAI name within the codec */
 	const char *codec_dai_name;
+	/*
+	 * You MAY specify the link's platform/PCM/DMA driver, either by
+	 * device name, or by DT/OF node, but not both. Some forms of link
+	 * do not need a platform.
+	 */
+	const char *platform_name;
+	const struct device_node *platform_of_node;
 	int be_id;	/* optional ID for machine driver BE identification */
 
 	const struct snd_soc_pcm_stream *params;