ASoC: stm32: add bindings for SAI

This patch adds documentation of device tree bindings for the
STM32 SAI ASoC driver.

Signed-off-by: olivier moysan <olivier.moysan@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/Documentation/devicetree/bindings/sound/st,stm32-sai.txt b/Documentation/devicetree/bindings/sound/st,stm32-sai.txt
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+STMicroelectronics STM32 Serial Audio Interface (SAI).
+
+The SAI interface (Serial Audio Interface) offers a wide set of audio protocols
+as I2S standards, LSB or MSB-justified, PCM/DSP, TDM, and AC'97.
+The SAI contains two independent audio sub-blocks. Each sub-block has
+its own clock generator and I/O lines controller.
+
+Required properties:
+  - compatible: Should be "st,stm32f4-sai"
+  - reg: Base address and size of SAI common register set.
+  - clocks: Must contain phandle and clock specifier pairs for each entry
+       in clock-names.
+  - clock-names: Must contain "x8k" and "x11k"
+       "x8k": SAI parent clock for sampling rates multiple of 8kHz.
+       "x11k": SAI parent clock for sampling rates multiple of 11.025kHz.
+  - interrupts: cpu DAI interrupt line shared by SAI sub-blocks
+
+Optional properties:
+  - resets: Reference to a reset controller asserting the SAI
+
+SAI subnodes:
+Two subnodes corresponding to SAI sub-block instances A et B can be defined.
+Subnode can be omitted for unsused sub-block.
+
+SAI subnodes required properties:
+  - compatible: Should be "st,stm32-sai-sub-a" or "st,stm32-sai-sub-b"
+       for SAI sub-block A or B respectively.
+  - reg: Base address and size of SAI sub-block register set.
+  - clocks: Must contain one phandle and clock specifier pair
+       for sai_ck which feeds the internal clock generator.
+  - clock-names: Must contain "sai_ck".
+  - dmas: see Documentation/devicetree/bindings/dma/stm32-dma.txt
+  - dma-names: identifier string for each DMA request line
+       "tx": if sai sub-block is configured as playback DAI
+       "rx": if sai sub-block is configured as capture DAI
+  - pinctrl-names: should contain only value "default"
+  - pinctrl-0: see Documentation/devicetree/bindings/pinctrl/pinctrl-stm32.txt
+
+Example:
+sound_card {
+       compatible = "audio-graph-card";
+       dais = <&sai1b_port>;
+};
+
+sai1: sai1@40015800 {
+       compatible = "st,stm32f4-sai";
+       #address-cells = <1>;
+       #size-cells = <1>;
+       ranges;
+       reg = <0x40015800 0x4>;
+       clocks = <&rcc 1 CLK_SAIQ_PDIV>, <&rcc 1 CLK_I2SQ_PDIV>;
+       clock-names = "x8k", "x11k";
+       interrupts = <87>;
+
+       sai1b: audio-controller@40015824 {
+               #sound-dai-cells = <0>;
+               compatible = "st,stm32-sai-sub-b";
+               reg = <0x40015824 0x1C>;
+               clocks = <&rcc 1 CLK_SAI2>;
+               clock-names = "sai_ck";
+               dmas = <&dma2 5 0 0x400 0x0>;
+               dma-names = "tx";
+               pinctrl-names = "default";
+               pinctrl-0 = <&pinctrl_sai1b>;
+
+               ports {
+                       #address-cells = <1>;
+                       #size-cells = <0>;
+
+                       sai1b_port: port@0 {
+                               reg = <0>;
+                               cpu_endpoint: endpoint {
+                                       remote-endpoint = <&codec_endpoint>;
+                                       audio-graph-card,format = "i2s";
+                                       audio-graph-card,bitclock-master = <&codec_endpoint>;
+                                       audio-graph-card,frame-master = <&codec_endpoint>;
+                               };
+                       };
+               };
+       };
+};
+
+audio-codec {
+       codec_port: port {
+               codec_endpoint: endpoint {
+                       remote-endpoint = <&cpu_endpoint>;
+               };
+       };
+};