Re: [PATCH 1/2] dt-bindings: iio: adc: add lltc,ltc2387

[Conor Dooley <conor@kernel.org>]

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On Tue, Oct 27, 2026 at 03:44:08PM +0200, Nicolae-Daniel Deaconescu wrote:
> From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> 
> Add bindings for the LTC2387-16 and LTC2387-18, 15 Msps SAR ADCs with
> an LVDS data interface, and for the ADAQ23875, ADAQ23876 and ADAQ23878
> uModule ADCs, which pair an LTC2387 die with a fully differential
> amplifier front end.
> 
> Conversion start (CNV) and the gated LVDS clock are driven by two PWM
> channels. Sample data is captured by an AXI ADC IP core, referenced
> through io-backends. adi,use-two-lanes selects two-lane output, and
> adi,gain-milli gives the front-end gain: fixed at 2 on the ADAQ23875,
> set by pin strapping on the ADAQ23876 and ADAQ23878.
> 
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> Co-developed-by: Nicolae-Daniel Deaconescu <Nicolae-daniel.Deaconescu@analog.com>
> Signed-off-by: Nicolae-Daniel Deaconescu <Nicolae-daniel.Deaconescu@analog.com>
> Assisted-by: Claude:claude-opus-5-5
> ---
>  .../bindings/iio/adc/lltc,ltc2387.yaml        | 138 ++++++++++++++++++
>  MAINTAINERS                                   |   8 +
>  2 files changed, 146 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/lltc,ltc2387.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/lltc,ltc2387.yaml b/Documentation/devicetree/bindings/iio/adc/lltc,ltc2387.yaml
> new file mode 100644
> index 000000000000..f912260c8f79
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/lltc,ltc2387.yaml
> @@ -0,0 +1,138 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +# Copyright 2022 Analog Devices Inc.
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/lltc,ltc2387.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Linear Technology / Analog Devices LTC2387 ADC
> +
> +maintainers:
> +  - Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> +  - Nicolae-Daniel Deaconescu <Nicolae-daniel.Deaconescu@analog.com>
> +
> +description: |
> +  The LTC2387-18 is a low noise, high speed, 18-bit 15Msps
> +  successive approximation register (SAR) ADC ideally
> +  suited for a wide range of applications.
> +
> +  https://www.analog.com/media/en/technical-documentation/data-sheets/238718fa.pdf
> +  https://www.analog.com/media/en/technical-documentation/data-sheets/238716f.pdf
> +
> +properties:
> +  compatible:
> +    enum:
> +      - adi,adaq23875
> +      - adi,adaq23876
> +      - adi,adaq23878
> +      - lltc,ltc2387-16
> +      - lltc,ltc2387-16-x4
> +      - lltc,ltc2387-18
> +      - lltc,ltc2387-18-x4

Why are we getting new devices with linear vendor prefixes? My
understanding was that new devices from ADI subsidiaries were to use the
adi vendor prefix.


> +
> +  clocks:
> +    description: Sampling clock
> +    maxItems: 1
> +
> +  pwms:
> +    maxItems: 2
> +    description:
> +      PWM signals used to synchronize the sampling procedure
> +
> +  pwm-names:
> +    items:
> +      - const: cnv
> +      - const: clk_gate

Hmm, ltc2387-16 does not appear to have these signals?
Well, it has "cnv" but "cnv" has "sample clock" as the input name so is
the clocks property above and pwm-clock can be used if the provider is a
pwm?

Either there's some mutual exclusion missing here or the modelling in
incorrect.

"clk_gate" doesn't appear in either of the datasheets I looked at, what
does that actually do?

pw-bot: changes-requested

> +
> +  io-backends:
> +    description:
> +      The AXI ADC IP block (axi_ltc2387) that captures the LVDS data stream.
> +    maxItems: 1
> +
> +  vref-supply:
> +    description:
> +      External voltage reference. When absent the device's internal 4.096 V
> +      reference is assumed.
> +
> +  adi,use-two-lanes:
> +    description: The device uses two lanes for data transfer
> +    type: boolean

Please explain how this is not determinable from the compatible.

Cheers,
Conor.

> +
> +  adi,gain-milli:
> +    description:
> +      Gain of the fully-differential amplifier that the ADAQ2387x modules
> +      integrate ahead of the LTC2387 die, expressed as gain * 1000. It is
> +      fixed on the ADAQ23875 and set by pin strapping on the ADAQ23876 and
> +      ADAQ23878, so it must match the board. The bare ltc2387-* parts have
> +      no amplifier.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [370, 730, 870, 1380, 2000, 2250]
> +
> +required:
> +  - compatible
> +  - clocks
> +  - io-backends
> +  - pwms
> +  - pwm-names
> +
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - lltc,ltc2387-16
> +              - lltc,ltc2387-16-x4
> +              - lltc,ltc2387-18
> +              - lltc,ltc2387-18-x4
> +    then:
> +      properties:
> +        adi,gain-milli: false
> +
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            const: adi,adaq23875
> +    then:
> +      properties:
> +        adi,gain-milli:
> +          const: 2000
> +
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - adi,adaq23876
> +              - adi,adaq23878
> +    then:
> +      properties:
> +        adi,gain-milli:
> +          enum: [370, 730, 870, 1380, 2250]
> +      required:
> +        - adi,gain-milli
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    adc {
> +            compatible = "lltc,ltc2387-16";
> +            clocks = <&clk 0>;
> +            io-backends = <&axi_adc>;
> +            pwms = <&pwm 0 0>, <&pwm 1 0>;
> +            pwm-names = "cnv", "clk_gate";
> +            vref-supply = <&vref>;
> +    };
> +  - |
> +    adc {
> +            compatible = "adi,adaq23878";
> +            clocks = <&clk 0>;
> +            io-backends = <&axi_adc>;
> +            pwms = <&pwm 0 0>, <&pwm 1 0>;
> +            pwm-names = "cnv", "clk_gate";
> +            vref-supply = <&vref>;
> +            adi,use-two-lanes;
> +            adi,gain-milli = <870>;
> +    };
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 52024397dc78..b871d7f25d76 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -15529,6 +15529,14 @@ W:	https://ez.analog.com/linux-software-drivers
>  F:	Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
>  F:	drivers/iio/adc/ltc2378.c
>  
> +LTC2387 IIO ADC DRIVER
> +M:	Nicolae-Daniel Deaconescu <Nicolae-daniel.Deaconescu@analog.com>
> +M:	Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> +L:	linux-iio@vger.kernel.org
> +S:	Supported
> +W:	https://ez.analog.com/linux-software-drivers
> +F:	Documentation/devicetree/bindings/iio/adc/lltc,ltc2387.yaml
> +
>  LTC2664 IIO DAC DRIVER
>  M:	Michael Hennerich <michael.hennerich@analog.com>
>  M:	Kim Seer Paller <kimseer.paller@analog.com>
> -- 
> 2.34.1
> 

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