ASoC: rsnd: add simplified module explanation

Renesas sound driver user needs to read its datasheet when create DT.
But it is difficult to understand, because it has many modules
(SRC/CTU/MIX/DVC/SSIU/SSI/AudioDMAC/AudioDMACperiperi),
and many features (Asynchronous/Synchronous mode on SRC, CTU matrix,
DVC volume settings feature, Multi-SSI/TDM-SSI, etc).
This patch adds simplified explanation to help setting/understanding.

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

Documentation/devicetree/bindings/sound/renesas,rsnd.txt

@@ -1,6 +1,337 @@
 Renesas R-Car sound
 
+=============================================
+* Modules
+=============================================
+
+Renesas R-Car sound is constructed from below modules
+(for Gen2 or later)
+
+ SCU		: Sampling Rate Converter Unit
+  - SRC		: Sampling Rate Converter
+  - CMD
+   - CTU	: Channel Transfer Unit
+   - MIX	: Mixer
+   - DVC	: Digital Volume and Mute Function
+ SSIU		: Serial Sound Interface Unit
+ SSI		: Serial Sound Interface
+
+See detail of each module's channels, connection, limitation on datasheet
+
+=============================================
+* Multi channel
+=============================================
+
+Multi channel is supported by Multi-SSI, or TDM-SSI.
+
+ Multi-SSI	: 6ch case, you can use stereo x 3 SSI
+ TDM-SSI	: 6ch case, you can use TDM
+
+=============================================
+* Enable/Disable each modules
+=============================================
+
+See datasheet to check SRC/CTU/MIX/DVC connect-limitation.
+DT controls enabling/disabling module.
+${LINUX}/arch/arm/boot/dts/r8a7790-lager.dts can be good example.
+This is example of
+
+Playback: [MEM] -> [SRC2] -> [DVC0] -> [SSIU0/SSI0] -> [codec]
+Capture:  [MEM] <- [DVC1] <- [SRC3] <- [SSIU1/SSI1] <- [codec]
+
+	&rcar_sound {
+		...
+		rcar_sound,dai {
+			dai0 {
+				playback = <&ssi0 &src2 &dvc0>;
+				capture  = <&ssi1 &src3 &dvc1>;
+			};
+		};
+	};
+
+You can use below.
+${LINUX}/arch/arm/boot/dts/r8a7790.dts can be good example.
+
+	&src0	&ctu00	&mix0	&dvc0	&ssi0
+	&src1	&ctu01	&mix1	&dvc1	&ssi1
+	&src2	&ctu02			&ssi2
+	&src3	&ctu03			&ssi3
+	&src4				&ssi4
+	&src5	&ctu10			&ssi5
+	&src6	&ctu11			&ssi6
+	&src7	&ctu12			&ssi7
+	&src8	&ctu13			&ssi8
+	&src9				&ssi9
+
+=============================================
+* SRC (Sampling Rate Converter)
+=============================================
+
+ [xx]Hz        [yy]Hz
+ ------> [SRC] ------>
+
+SRC can convert [xx]Hz to [yy]Hz. Then, it has below 2 modes
+
+ Asynchronous mode:	input data / output data are based on different clocks.
+			you can use this mode on Playback / Capture
+ Synchronous mode:	input data / output data are based on same clocks.
+			This mode will be used if system doesn't have its input clock,
+			for example digital TV case.
+			you can use this mode on Playback
+
+------------------
+**     Asynchronous mode
+------------------
+
+You need to use "renesas,rsrc-card" sound card for it.
+example)
+
+	sound {
+		compatible = "renesas,rsrc-card";
+		...
+		/*
+		 * SRC Asynchronous mode setting
+		 * Playback:
+		 * All input data will be converted to 48kHz
+		 * Capture:
+		 * Inputed 48kHz data will be converted to
+		 * system specified Hz
+		 */
+		convert-rate = <48000>;
+		...
+		cpu {
+			sound-dai = <&rcar_sound>;
+		};
+		codec {
+			...
+		};
+	};
+
+------------------
+**     Synchronous mode
+------------------
+
+	> amixer set "SRC Out Rate" on
+	> aplay xxxx.wav
+	> amixer set "SRC Out Rate" 48000
+	> amixer set "SRC Out Rate" 44100
+
+=============================================
+* CTU (Channel Transfer Unit)
+=============================================
+
+ [xx]ch        [yy]ch
+ ------> [CTU] -------->
+
+CTU can convert [xx]ch to [yy]ch, or exchange outputed channel.
+CTU conversion needs matrix settings.
+For more detail information, see below
+
+	Renesas R-Car datasheet
+	 - Sampling Rate Converter Unit (SCU)
+	  - SCU Operation
+	   - CMD Block
+	    - Functional Blocks in CMD
+
+	Renesas R-Car datasheet
+	 - Sampling Rate Converter Unit (SCU)
+	  - Register Description
+	   - CTUn Scale Value exx Register (CTUn_SVxxR)
+
+	${LINUX}/sound/soc/sh/rcar/ctu.c
+	 - comment of header
+
+You need to use "renesas,rsrc-card" sound card for it.
+example)
+
+	sound {
+		compatible = "renesas,rsrc-card";
+		...
+		/*
+		 * CTU setting
+		 * All input data will be converted to 2ch
+		 * as output data
+		 */
+		convert-channels = <2>;
+		...
+		cpu {
+			sound-dai = <&rcar_sound>;
+		};
+		codec {
+			...
+		};
+	};
+
+Ex) Exchange output channel
+ Input -> Output
+  1ch  ->  0ch
+  0ch  ->  1ch
+
+  example of using matrix
+	output 0ch = (input 0ch x 0) + (input 1ch x 1)
+	output 1ch = (input 0ch x 1) + (input 1ch x 0)
+
+	amixer set "CTU Reset" on
+	amixer set "CTU Pass" 9,10
+	amixer set "CTU SV0" 0,4194304
+	amixer set "CTU SV1" 4194304,0
+
+ example of changing connection
+	amixer set "CTU Reset" on
+	amixer set "CTU Pass" 2,1
+
+=============================================
+* MIX (Mixer)
+=============================================
+
+MIX merges 2 sounds path. You can see 2 sound interface on system,
+and these sounds will be merged by MIX.
+
+	aplay -D plughw:0,0 xxxx.wav &
+	aplay -D plughw:0,1 yyyy.wav
+
+You need to use "renesas,rsrc-card" sound card for it.
+Ex)
+	[MEM] -> [SRC1] -> [CTU02] -+-> [MIX0] -> [DVC0] -> [SSI0]
+	                            |
+	[MEM] -> [SRC2] -> [CTU03] -+
+
+	sound {
+		compatible = "renesas,rsrc-card";
+		...
+		cpu@0 {
+			sound-dai = <&rcar_sound 0>;
+		};
+		cpu@1 {
+			sound-dai = <&rcar_sound 1>;
+		};
+		codec {
+			...
+		};
+	};
+
+	&rcar_sound {
+		...
+		rcar_sound,dai {
+			dai0 {
+				playback = <&src1 &ctu02 &mix0 &dvc0 &ssi0>;
+			};
+			dai1 {
+				playback = <&src2 &ctu03 &mix0 &dvc0 &ssi0>;
+			};
+		};
+	};
+
+=============================================
+* DVC (Digital Volume and Mute Function)
+=============================================
+
+DVC controls Playback/Capture volume.
+
+Playback Volume
+	amixer set "DVC Out" 100%
+
+Capture Volume
+	amixer set "DVC In" 100%
+
+Playback Mute
+	amixer set "DVC Out Mute" on
+
+Capture Mute
+	amixer set "DVC In Mute" on
+
+Volume Ramp
+	amixer set "DVC Out Ramp Up Rate"   "0.125 dB/64 steps"
+	amixer set "DVC Out Ramp Down Rate" "0.125 dB/512 steps"
+	amixer set "DVC Out Ramp" on
+	aplay xxx.wav &
+	amixer set "DVC Out"  80%  // Volume Down
+	amixer set "DVC Out" 100%  // Volume Up
+
+=============================================
+* SSIU (Serial Sound Interface Unit)
+=============================================
+
+There is no DT settings for SSIU, because SSIU will be automatically
+selected via SSI.
+SSIU can avoid some under/over run error, because it has some buffer.
+But you can't use it if SSI was PIO mode.
+In DMA mode, you can select not to use SSIU by using "no-busif" on DT.
+
+	&ssi0 {
+		no-busif;
+	};
+
+=============================================
+* SSI (Serial Sound Interface)
+=============================================
+
+**  PIO mode
+
+You can use PIO mode which is for connection check by using.
+Note: The system will drop non-SSI modules in PIO mode
+even though if DT is selecting other modules.
+
+	&ssi0 {
+		pio-transfer
+	};
+
+** DMA mode without SSIU
+
+You can use DMA without SSIU.
+Note: under/over run, or noise are likely to occur
+
+	&ssi0 {
+		no-busif;
+	};
+
+** PIN sharing
+
+Each SSI can share WS pin. It is based on platform.
+This is example if SSI1 want to share WS pin with SSI0
+
+	&ssi1 {
+		shared-pin;
+	};
+
+** Multi-SSI
+
+You can use Multi-SSI.
+This is example of SSI0/SSI1/SSI2 (= for 6ch)
+
+	&rcar_sound {
+		...
+		rcar_sound,dai {
+			dai0 {
+				playback = <&ssi0 &ssi1 &ssi2 &src0 &dvc0>;
+			};
+		};
+	};
+
+** TDM-SSI
+
+You can use TDM with SSI.
+This is example of TDM 6ch.
+Driver can automatically switches TDM <-> stereo mode in this case.
+
+	rsnd_tdm: sound {
+		compatible = "simple-audio-card";
+		...
+		simple-audio-card,cpu {
+			/* system can use TDM 6ch */
+			dai-tdm-slot-num = <6>;
+			sound-dai = <&rcar_sound>;
+		};
+		simple-audio-card,codec {
+			...
+		};
+	};
+
+
+=============================================
 Required properties:
+=============================================
+
 - compatible			: "renesas,rcar_sound-<soctype>", fallbacks
 				  "renesas,rcar_sound-gen1" if generation1, and
 				  "renesas,rcar_sound-gen2" if generation2
@@ -64,7 +395,10 @@ DAI subnode properties:
 - playback			: list of playback modules
 - capture			: list of capture  modules
 
+
+=============================================
 Example:
+=============================================
 
 rcar_sound: sound@ec500000 {
 	#sound-dai-cells = <1>;
@@ -250,7 +584,9 @@ rcar_sound: sound@ec500000 {
 	};
 };
 
+=============================================
 Example: simple sound card
+=============================================
 
 	rsnd_ak4643: sound {
 		compatible = "simple-audio-card";
@@ -290,7 +626,9 @@ Example: simple sound card
 	shared-pin;
 };
 
+=============================================
 Example: simple sound card for TDM
+=============================================
 
 	rsnd_tdm: sound {
 		compatible = "simple-audio-card";
@@ -309,7 +647,9 @@ Example: simple sound card for TDM
 		};
 	};
 
+=============================================
 Example: simple sound card for Multi channel
+=============================================
 
 &rcar_sound {
 	pinctrl-0 = <&sound_pins &sound_clk_pins>;

sound/soc/sh/rcar/dvc.c

@@ -8,6 +8,29 @@
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
+
+/*
+ * Playback Volume
+ *	amixer set "DVC Out" 100%
+ *
+ * Capture Volume
+ *	amixer set "DVC In" 100%
+ *
+ * Playback Mute
+ *	amixer set "DVC Out Mute" on
+ *
+ * Capture Mute
+ *	amixer set "DVC In Mute" on
+ *
+ * Volume Ramp
+ *	amixer set "DVC Out Ramp Up Rate"   "0.125 dB/64 steps"
+ *	amixer set "DVC Out Ramp Down Rate" "0.125 dB/512 steps"
+ *	amixer set "DVC Out Ramp" on
+ *	aplay xxx.wav &
+ *	amixer set "DVC Out"  80%  // Volume Down
+ *	amixer set "DVC Out" 100%  // Volume Up
+ */
+
 #include "rsnd.h"
 
 #define RSND_DVC_NAME_SIZE	16