ASoC: rsnd: add detail explanation of L/R conversion timing

Renesas Sound device *Hardware* L/R and Linux *Software* L/R are
inverted. Because of this background, it needs to convert L/R.
Then, DVC needs *Hardware* L/R, and Linux needs *Software* L/R.
Because Playback/Capture needs different timing, and there is no
explanation about it on source code / git log, this patch adds it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/sound/soc/sh/rcar/core.c b/sound/soc/sh/rcar/core.c
index 7c68f9d4a0ed..1bf261d677b7 100644
--- a/sound/soc/sh/rcar/core.c
+++ b/sound/soc/sh/rcar/core.c
@@ -310,6 +310,24 @@ u32 rsnd_get_dalign(struct rsnd_mod *mod, struct rsnd_dai_stream *io)
         u32 val = 0x76543210;
         u32 mask = ~0;
 
+        /*
+         * *Hardware* L/R and *Software* L/R are inverted.
+         * We need to care about inversion timing to control
+         * Playback/Capture correctly.
+         * The point is [DVC] needs *Hardware* L/R, [MEM] needs *Software* L/R
+         *
+         * sL/R : software L/R
+         * hL/R : hardware L/R
+         * (*)  : conversion timing
+         *
+         * Playback
+         *           sL/R (*) hL/R     hL/R     hL/R      hL/R     hL/R
+         *      [MEM] -> [SRC] -> [DVC] -> [CMD] -> [SSIU] -> [SSI] -> codec
+         *
+         * Capture
+         *           hL/R     hL/R      hL/R     hL/R     hL/R (*) sL/R
+         *      codec -> [SSI] -> [SSIU] -> [SRC] -> [DVC] -> [CMD] -> [MEM]
+         */
         if (rsnd_io_is_play(io)) {
                 struct rsnd_mod *src = rsnd_io_to_mod_src(io);