linux-kernel - Re: [PATCH 1/6] dt-bindings: ROHM BD79104 ADC

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Message-ID: <20250331-chooser-superbowl-2dfa754e8d05@spud>
Date: Mon, 31 Mar 2025 16:47:29 +0100
From: Conor Dooley <conor@...nel.org>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Nuno Sa <nuno.sa@...log.com>,
	David Lechner <dlechner@...libre.com>,
	Javier Carrasco <javier.carrasco.cruz@...il.com>,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] dt-bindings: ROHM BD79104 ADC

On Mon, Mar 31, 2025 at 11:02:20AM +0300, Matti Vaittinen wrote:
> The ROHM BD79104 is a 12-bit, 8-channel ADC with two power supply pins,
> connected to SPI. It's worth noting the IC requires SPI MODE 3, (CPHA =
> 1, CPOL = 1).
> 
> I used an evaluation board "BD79104FV-EVK-001" from ROHM. With this
> board I had problems to have things working correctly with higher SPI
> clock frequencies. I didn't do thorough testing for maximum frequency
> though. First attempt was 40M, then 20M and finally 4M. With 20M it
> seemed as if the read values were shifted by 1 bit. With 4M it worked
> fine.
> 
> The component data-sheet is not exact what comes to the maximum SPI
> frequency. It says SPI frequency is 20M - "unless othervice specified".
> Additionally, it says that maximum sampling rate is 1Mhz, and since
> reading a sample requires writing the channel (16 bits) and reading
> data (16 bits) - we get some upper limit from this.
> 
> From the "frequency is 20M, unless othervice specified" I picked the
> maximum frequency 20M - and did assumption that my problems with 20M
> weren't related to the BD79104 - but to the evaluation board
> "BD79104FV-EVK-001".
> 
> Add bindings for the ROHM BD79104 ADC.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>

Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

> ---
>  .../bindings/iio/adc/rohm,bd79104.yaml        | 69 +++++++++++++++++++
>  1 file changed, 69 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml b/Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml
> new file mode 100644
> index 000000000000..2a8ad4fdfc6b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/rohm,bd79104.yaml
> @@ -0,0 +1,69 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/rohm,bd79104.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: ROHM Semiconductor BD79104 ADC
> +
> +maintainers:
> +  - Matti Vaittinen <mazziesaccount@...il.com>
> +
> +description: |
> +  12 bit SPI ADC with 8 channels.
> +
> +properties:
> +  compatible:
> +    const: rohm,bd79104
> +
> +  reg:
> +    maxItems: 1
> +
> +  vdd-supply: true
> +  iovdd-supply: true
> +
> +# The component data-sheet says the frequency is 20M. I, however, found
> +# that the ROHM evaluation board BD79104FV-EVK-001 had problems with 20M.
> +# I have successfully used it with 4M. My _assumption_ is that this is not
> +# the limitation of the component itself, but a limitation of the EVK.
> +  spi-max-frequency:
> +    maximum: 20000000
> +
> +  "#io-channel-cells":
> +    const: 1
> +
> +  spi-cpha: true
> +  spi-cpol: true
> +
> +required:
> +  - compatible
> +  - reg
> +  - vdd-supply
> +  - iovdd-supply
> +  - spi-cpha
> +  - spi-cpol
> +
> +allOf:
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/interrupt-controller/irq.h>
> +    spi {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@0 {
> +            compatible = "rohm,bd79104";
> +            reg = <0>;
> +            vdd-supply = <&vdd_supply>;
> +            iovdd-supply = <&iovdd_supply>;
> +            spi-max-frequency = <4000000>;
> +            spi-cpha;
> +            spi-cpol;
> +            #io-channel-cells = <1>;
> +        };
> +    };
> +...
> -- 
> 2.48.1
> 



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