[PATCH v2 4/7] dt-bindings:iio:resolver: Add docs for ad2s90

[Ardelean, Alexandru]

On Sun, 2018-11-18 at 02:25 -0200, Matheus Tavares wrote:
> This patch adds the device tree binding documentation for the ad2s90
> resolver-to-digital converter.
> 

One minor comment inline.

> Signed-off-by: Matheus Tavares <matheus.bernardino at usp.br>
> ---
> Changes in v2:
>  - Rewritten 'spi-cpol and spi-cpha' item to say that the device can
>  work in either mode (0,0) or (1,1) and explain how they should be
>  specified in DT.
> 
>  .../bindings/iio/resolver/ad2s90.txt          | 28 +++++++++++++++++++
>  1 file changed, 28 insertions(+)
>  create mode 100644
> Documentation/devicetree/bindings/iio/resolver/ad2s90.txt
> 
> diff --git a/Documentation/devicetree/bindings/iio/resolver/ad2s90.txt
> b/Documentation/devicetree/bindings/iio/resolver/ad2s90.txt
> new file mode 100644
> index 000000000000..594417539938
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/resolver/ad2s90.txt
> @@ -0,0 +1,28 @@
> +Analog Devices AD2S90 Resolver-to-Digital Converter
> +
> +https://www.analog.com/en/products/ad2s90.html
> +
> +Required properties:
> +  - compatible: should be "adi,ad2s90"
> +  - reg: SPI chip select number for the device
> +  - spi-max-frequency: set maximum clock frequency, must be 830000
> +  - spi-cpol and spi-cpha:
> +        Either SPI mode (0,0) or (1,1) must be used, so specify none or
> both of
> +        spi-cpha, spi-cpol.
For SPI properties it's a good idea to also reference the document for SPI
bindings.
Something like:
    See for more details:
     Documentation/devicetree/bindings/spi/spi-bus.txt

> +
> +Note about max frequency:
> +    Chip's max frequency, as specified in its datasheet, is 2Mhz. But a
> 600ns
> +    delay is expected between the application of a logic LO to CS and
> the
> +    application of SCLK, as also specified. And since the delay is not
> +    implemented in the spi code, to satisfy it, SCLK's period should be
> at most
> +    2 * 600ns, so the max frequency should be 1 / (2 * 6e-7), which
> gives
> +    roughly 830000Hz.
> +
> +Example:
> +resolver at 0 {
> +	compatible = "adi,ad2s90";
> +	reg = <0>;
> +	spi-max-frequency = <830000>;
> +	spi-cpol;
> +	spi-cpha;
> +};