linux-kernel - Re: [PATCH 1/2] dt-bindings: iio: adc: Add TI ADS1018/ADS1118

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Message-Id: <DEESPC8XZSXI.3G1JISSNEBC3Q@gmail.com>
Date: Fri, 21 Nov 2025 19:26:24 -0500
From: "Kurt Borja" <kuurtb@...il.com>
To: "David Lechner" <dlechner@...libre.com>, "Kurt Borja"
 <kuurtb@...il.com>, "Jonathan Cameron" <jic23@...nel.org>, "Rob Herring"
 <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>, "Conor
 Dooley" <conor+dt@...nel.org>, "Tobias Sperling"
 <tobias.sperling@...ting.com>
Cc: Nuno Sá <nuno.sa@...log.com>, "Andy Shevchenko"
 <andy@...nel.org>, <linux-iio@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Jonathan
 Cameron" <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH 1/2] dt-bindings: iio: adc: Add TI ADS1018/ADS1118

On Fri Nov 21, 2025 at 5:32 PM -05, David Lechner wrote:
> On 11/21/25 11:16 AM, Kurt Borja wrote:
>> Add documentation for Texas Instruments ADS1018 and ADS1118
>> analog-to-digital converters.
>> 
>> Signed-off-by: Kurt Borja <kuurtb@...il.com>
>> ---
>>  .../devicetree/bindings/iio/adc/ti,ads1118.yaml    | 132 +++++++++++++++++++++
>>  1 file changed, 132 insertions(+)
>> 
>> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1118.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1118.yaml
>> new file mode 100644
>> index 000000000000..eb7228ed6ddb
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1118.yaml
>
> I like to make the file name match the lowest number. That way it matches
> the first item in the compatible list.
>
>> @@ -0,0 +1,132 @@
>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>
> Better to be specific with GPL-2.0-only or GPL-2.0-or-later (your choice).

I will go for GPL-2.0-only on both files.

>
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/iio/adc/ti,ads1118.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: TI ADS1018/ADS1118 SPI analog to digital converter
>> +
>> +maintainers:
>> +  - Kurt Borja <kuurtb@...il.com>
>> +
>> +description: |
>> +  The ADS1018/ADS1118 is a precision, low-power, 12-bit or 16-bit, noise-free,
>> +  analog-to-digital converter (ADC). It integrates a programmable gain amplifier
>> +  (PGA), voltage reference, oscillator and high-accuracy temperature sensor.
>> +
>> +  Datasheets:
>> +    - ADS1018: https://www.ti.com/lit/ds/symlink/ads1018.pdf
>> +    - ADS1118: https://www.ti.com/lit/ds/symlink/ads1118.pdf
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - ti,ads1018
>> +      - ti,ads1118
>> +
>> +  reg:
>> +    maxitems: 1
>
> We know the max SCLK rate from the datasheet, so we can add:
>
> spi-max-frequency:
>   maximum: 4000000
>
> And we need to explicitly mention this one (it isn't part of
> spi-peripheral-props.yaml but rather comes from spi-controller.yaml):
>
> spi-cpha: true
>
>> +
>> +  interrupts:
>> +    description: DOUT/DRDY (Data Out/Data Ready) line.
>> +    maxitems: 1
>> +
>> +  drdy-gpios:
>> +    description:
>> +      Extra GPIO line connected to DOUT/DRDY (Data Out/Data Ready). This allows
>> +      distinguishing between latched and real DRDY IRQs.
>> +    maxitems: 1
>> +
>> +  '#address-cells':
>> +    const: 1
>> +
>> +  '#size-cells':
>> +    const: 0
>> +
>> +  '#io-channel-cells':
>> +    const: 1
>> +
>
> All chips need power, so we should have:
>
> vdd-supply: true
>
> and make it required.
>
>> +required:
>> +  - compatible
>> +  - reg
>> +  - drdy-gpios
>
> The chip can be used without needing the DRDY signal, so drdy-gpios and
> interrupts should not be required.
>
>> +  - '#address-cells'
>> +  - '#size-cells'
>> +
>> +patternProperties:
>> +  "^channel@[0-7]$":
>> +    type: object
>> +    $ref: /schemas/iio/adc/adc.yaml#
>> +    description: Properties for a single ADC channel.
>> +
>> +    properties:
>> +      reg:
>> +        minimum: 0
>> +        maximum: 7
>> +        description: The channel index (0-7).
>> +
>> +      ti,gain:
>> +        $ref: /schemas/types.yaml#/definitions/uint32
>> +        minimum: 0
>> +        maximum: 5
>> +        description:
>> +          Programmable gain amplifier configuration, as described in the PGA
>> +          Config Register Field description. If not present, the default is
>> +          used.
>
> The gain is programmable, so normally, we would set that by writing
> to the in_voltageY_scale attribute rather than hard-coding it in the
> devicetree.
>
>> +
>> +      ti,datarate:
>> +        $ref: /schemas/types.yaml#/definitions/uint32
>> +        minimum: 0
>> +        maximum: 7
>> +        description:
>> +          Data rate configuration, as described in the DR Config Register Field
>> +          description. If not present, the default is used.
>
> Likewise, the data rate should be set at runtime using a
> sampling_frequency attribute rather than being hard-coded
> in the devicetree.

I actually took this approach from ti-ads1015. I was debating this
myself.

I'll gladly drop these.

>
>> +
>> +    required:
>> +      - reg
>> +
>> +    additionalProperties: false
>> +
> So we shouldn't need explicit channel properties at this time.

Ack for the rest of comments.


-- 
 ~ Kurt