IIO: add DT bindings for stm32 DFSDM filter

STMicroelectronics STM32 DFSDM ADC device driver

STM32 DFSDM ADC is a sigma delta analog-to-digital converter dedicated to

interface external sigma delta modulators to STM32 micro controllers.

It is mainly targeted for:

- Sigma delta modulators (motor control, metering...)

- PDM microphones (audio digital microphone)

It features up to 8 serial digital interfaces (SPI or Manchester) and

up to 4 filters on stm32h7.

Each child node match with a filter instance.

Contents of a STM32 DFSDM root node:

------------------------------------

Required properties:

- compatible: Should be "st,stm32h7-dfsdm".

- reg: Offset and length of the DFSDM block register set.

- clocks: IP and serial interfaces clocking. Should be set according

		to rcc clock ID and "clock-names".

- clock-names: Input clock name "dfsdm" must be defined,

		"audio" is optional. If defined CLKOUT is based on the audio

		clock, else "dfsdm" is used.

- #interrupt-cells = <1>;

- #address-cells = <1>;

- #size-cells = <0>;

Optional properties:

- spi-max-frequency: Requested only for SPI master mode.

		  SPI clock OUT frequency (Hz). This clock must be set according

		  to "clock" property. Frequency must be a multiple of the rcc

		  clock frequency. If not, SPI CLKOUT frequency will not be

		  accurate.

Contents of a STM32 DFSDM child nodes:

--------------------------------------

Required properties:

- compatible: Must be:

	"st,stm32-dfsdm-adc" for sigma delta ADCs

	"st,stm32-dfsdm-dmic" for audio digital microphone.

- reg: Specifies the DFSDM filter instance used.

- interrupts: IRQ lines connected to each DFSDM filter instance.

- st,adc-channels:	List of single-ended channels muxed for this ADC.

			valid values:

				"st,stm32h7-dfsdm" compatibility: 0 to 7.

- st,adc-channel-names:	List of single-ended channel names.

- st,filter-order:  SinC filter order from 0 to 5.

			0: FastSinC

			[1-5]: order 1 to 5.

			For audio purpose it is recommended to use order 3 to 5.

- #io-channel-cells = <1>: See the IIO bindings section "IIO consumers".

Required properties for "st,stm32-dfsdm-adc" compatibility:

- io-channels: From common IIO binding. Used to pipe external sigma delta

		modulator or internal ADC output to DFSDM channel.

		This is not required for "st,stm32-dfsdm-pdm" compatibility as

		PDM microphone is binded in Audio DT node.

Required properties for "st,stm32-dfsdm-pdm" compatibility:

- #sound-dai-cells: Must be set to 0.

- dma: DMA controller phandle and DMA request line associated to the

		filter instance (specified by the field "reg")

- dma-names: Must be "rx"

Optional properties:

- st,adc-channel-types:	Single-ended channel input type.

			- "SPI_R": SPI with data on rising edge (default)

			- "SPI_F": SPI with data on falling edge

			- "MANCH_R": manchester codec, rising edge = logic 0

			- "MANCH_F": manchester codec, falling edge = logic 1

- st,adc-channel-clk-src: Conversion clock source.

			  - "CLKIN": external SPI clock (CLKIN x)

			  - "CLKOUT": internal SPI clock (CLKOUT) (default)

			  - "CLKOUT_F": internal SPI clock divided by 2 (falling edge).

			  - "CLKOUT_R": internal SPI clock divided by 2 (rising edge).

- st,adc-alt-channel: Must be defined if two sigma delta modulator are

			  connected on same SPI input.

			  If not set, channel n is connected to SPI input n.

			  If set, channel n is connected to SPI input n + 1.

- st,filter0-sync: Set to 1 to synchronize with DFSDM filter instance 0.

		   Used for multi microphones synchronization.

Example of a sigma delta adc connected on DFSDM SPI port 0

and a pdm microphone connected on DFSDM SPI port 1:

	ads1202: simple_sd_adc@0 {

		compatible = "ads1202";

		#io-channel-cells = <1>;

	};

	dfsdm: dfsdm@40017000 {

		compatible = "st,stm32h7-dfsdm";

		reg = <0x40017000 0x400>;

		clocks = <&rcc DFSDM1_CK>;

		clock-names = "dfsdm";

		#interrupt-cells = <1>;

		#address-cells = <1>;

		#size-cells = <0>;

		dfsdm_adc0: filter@0 {

			compatible = "st,stm32-dfsdm-adc";

			#io-channel-cells = <1>;

			reg = <0>;

			interrupts = <110>;

			st,adc-channels = <0>;

			st,adc-channel-names = "sd_adc0";

			st,adc-channel-types = "SPI_F";

			st,adc-channel-clk-src = "CLKOUT";

			io-channels = <&ads1202 0>;

			st,filter-order = <3>;

		};

		dfsdm_pdm1: filter@1 {

			compatible = "st,stm32-dfsdm-dmic";

			reg = <1>;

			interrupts = <111>;

			dmas = <&dmamux1 102 0x400 0x00>;

			dma-names = "rx";

			st,adc-channels = <1>;

			st,adc-channel-names = "dmic1";

			st,adc-channel-types = "SPI_R";

			st,adc-channel-clk-src = "CLKOUT";

			st,filter-order = <5>;

		};

	}