[RFC v2 6/7] IIO: add bindings for stm32 DFSDM filter

[Rob Herring]

On Mon, Feb 13, 2017 at 05:38:28PM +0100, Arnaud Pouliquen wrote:
> Add bindings that describe Digital Filter for Sigma Delta
> Modulators. DFSDM allows to connect sigma delta
> modulators and/or PDM microphones.
> 
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen at st.com>
> ---
>  .../bindings/iio/adc/st,stm32-dfsdm-adc.txt        | 125 +++++++++++++++++++++
>  1 file changed, 125 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/st,stm32-dfsdm-adc.txt
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/st,stm32-dfsdm-adc.txt b/Documentation/devicetree/bindings/iio/adc/st,stm32-dfsdm-adc.txt
> new file mode 100644
> index 0000000..83937cb
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/st,stm32-dfsdm-adc.txt
> @@ -0,0 +1,125 @@
> +STMicroelectronics STM32 DFSDM ADC device driver
> +
> +
> +STM32 DFSDM ADC is a sigma delta analog-to-digital converter dedicted to
> +interface external sigma delta modulators to stm32 micro controlers.
> +it is mainly targeted for:
> +- Sigma delta modulators ( motor control, metering...)
> +- PDM microphones ( audio digital microphone)
> +
> +It featured with up to 8 serial digital interface (SPI or Manchester) and
> +up to 4 filters.
> +
> +Each instance of the sub-drivers uses one filter instance.
> +
> +Contents of a stm32 dfsdmc root node:
> +-------------------------------------
> +Required properties:
> +- compatible: Should be "st,stm32-dfsdm-adc".
> +- 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.
> +- clocks: Clock for the analog circuitry (common to all ADCs).
> +- clock-names: Must be "adc".
> +
> +Optional properties:
> +- st,clkout-freq: needed 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, clkout frequency will not be
> +		  accurate.

We already have a standard property to specify the SPI freq.

> +
> +Contents of a stm32 DFSDM child nodes:
> +----------------------------------------
> +
> +Required properties:
> +- compatible: Must be:
> +	"st,stm32-dfsdm-adc" for sigma delta ADCs
> +	"st,stm32-dfsdm-pdm" for audio digital microphone.
> +- reg: Specifies the DFSDM filter instance.
> +- interrupts: IRQ lines connected to each DFSDM filter instance.
> +- st,adc-channels:	List of single-ended channels muxed for this ADC.
> +- st,adc-channel-names:	List of single-ended channels Name.

Why do you need names?

> +- st,dai-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.
> +
> +Required properties for "st,stm32-dfsdm-adc" compatibility:
> +- #io-channel-cells = <1>: See the IIO bindings section "IIO consumers".
> +- io-channels: from common iio binding. use to pipe external sigma delta
> +		modulator or internal ADC output to dfsdm channel.
> +
> +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. Default value is 0.

How is the default 0 when the values are strings?

> +			- "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. default value is 1.

Ditto.

Perhaps you should be using the clock binding and assigned-clocks 
property.

> +			  - "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.
> +		   to used for multi microphone synchronization.

Is there an instance 1?  If not, drop the 0. If you need to expand to 
multiple instances, you can have multiple values.

> +
> +Example of a sigma delta adc purpose:
> +	ads1202: simple_sd_adc at 0 {
> +		compatible = "sd-modulator";
> +		#io-channel-cells = <1>;
> +		status = "okay";
> +	};
> +	dfsdm: dfsdm at 40017000 {
> +		compatible = "st,stm32h7-dfsdm";
> +		reg = <0x40017000 0x400>;
> +		clocks = <&timer_clk>;
> +		clock-names = "dfsdm";
> +
> +		dfsdm_adc0: dfsdm-adc0 at 0 {
> +			compatible = "st,stm32-dfsdm-adc";
> +			#io-channel-cells = <1>;
> +			reg = <0>;
> +			interrupts = <110>;
> +			st,adc-channels = <0>;

Does reg provide the same thing?

> +			st,adc-channel-names = "in0";
> +			st,adc-channel-types = "SPI_R";
> +			st,adc-channel-clk-src = "CLKOUT";
> +			io-channels = <&ads1202 0>;
> +	};
> +
> +Example of a pdm microphone purpose:
> +	dfsdm: dfsdm at 40017000 {
> +		compatible = "st,stm32h7-dfsdm";
> +		reg = <0x40017000 0x400>;
> +		clocks = <&timer_clk>;
> +		clock-names = "dfsdm";
> +
> +		dfsdm_pdm0: dfsdm-pdm at 0 {
> +			compatible = "st,stm32-dfsdm-pdm";
> +			#sound-dai-cells = <0>;
> +			reg = <0>;
> +			interrupts = <110>;
> +			dmas = <&dmamux1 102 0x400 0x00>;
> +			dma-names = "rx";
> +			st,adc-channels = <0>;
> +			st,adc-channel-names = "pdm1";
> +			st,adc-channel-types = "SPI_R";
> +			st,adc-channel-clk-src = "CLKOUT";
> +		};
> +	}
> -- 
> 1.9.1
>