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>;
		};
	};
};