ASoC: stm32: Document STM32 I2S bindings

STMicroelectronics STM32 SPI/I2S Controller

The SPI/I2S block supports I2S/PCM protocols when configured on I2S mode.

Only some SPI instances support I2S.

Required properties:

  - compatible: Must be "st,stm32h7-i2s"

  - reg: Offset and length of the device's register set.

  - interrupts: Must contain the interrupt line id.

  - clocks: Must contain phandle and clock specifier pairs for each entry

	in clock-names.

  - clock-names: Must contain "i2sclk", "pclk", "x8k" and "x11k".

	"i2sclk": clock which feeds the internal clock generator

	"pclk": clock which feeds the peripheral bus interface

	"x8k": I2S parent clock for sampling rates multiple of 8kHz.

	"x11k": I2S parent clock for sampling rates multiple of 11.025kHz.

  - dmas: DMA specifiers for tx and rx dma.

    See Documentation/devicetree/bindings/dma/stm32-dma.txt.

  - dma-names: Identifier for each DMA request line. Must be "tx" and "rx".

  - pinctrl-names: should contain only value "default"

  - pinctrl-0: see Documentation/devicetree/bindings/pinctrl/pinctrl-stm32.txt

Optional properties:

  - resets: Reference to a reset controller asserting the reset controller

The device node should contain one 'port' child node with one child 'endpoint'

node, according to the bindings defined in Documentation/devicetree/bindings/

graph.txt.

Example:

sound_card {

	compatible = "audio-graph-card";

	dais = <&i2s2_port>;

};

i2s2: audio-controller@40003800 {

	compatible = "st,stm32h7-i2s";

	reg = <0x40003800 0x400>;

	interrupts = <36>;

	clocks = <&rcc PCLK1>, <&rcc SPI2_CK>, <&rcc PLL1_Q>, <&rcc PLL2_P>;

	clock-names = "pclk", "i2sclk",  "x8k", "x11k";

	dmas = <&dmamux2 2 39 0x400 0x1>,

           <&dmamux2 3 40 0x400 0x1>;

	dma-names = "rx", "tx";

	pinctrl-names = "default";

	pinctrl-0 = <&pinctrl_i2s2>;

	i2s2_port: port@0 {

		cpu_endpoint: endpoint {

			remote-endpoint = <&codec_endpoint>;

			format = "i2s";

		};

	};

};

audio-codec {

	codec_port: port@0 {

		codec_endpoint: endpoint {

			remote-endpoint = <&cpu_endpoint>;

		};

	};

};