[PATCH 1/3] dt-bindings: iio: adc: add bindings for stm32 mdf filter
Krzysztof Kozlowski
krzk at kernel.org
Fri Oct 2 02:22:29 PDT 2026
On Thu, Oct 01, 2026 at 04:56:45PM +0200, Olivier Moysan wrote:
> Add bindings that describes STM32 MDF settings to support
> digital filtering for Pulse Density Modulation (PDM) microphones
> and analog sigma delta modulators.
You already received review, so a few things on top to spare you one
more cycle:
A nit, subject: drop second/last, redundant "bindings for". The
"dt-bindings" prefix is already stating that these are bindings.
See also:
https://elixir.bootlin.com/linux/v7.1-rc7/source/Documentation/devicetree/bindings/submitting-patches.rst#L23
>
> Signed-off-by: Olivier Moysan <olivier.moysan at foss.st.com>
> ---
> .../bindings/iio/adc/st,stm32-mdf-adc.yaml | 383 ++++++++++++++++++
> 1 file changed, 383 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/iio/adc/st,stm32-mdf-adc.yaml
>
> diff --git a/Documentation/devicetree/bindings/iio/adc/st,stm32-mdf-adc.yaml b/Documentation/devicetree/bindings/iio/adc/st,stm32-mdf-adc.yaml
> new file mode 100644
> index 000000000000..f2fbc3e150e8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/st,stm32-mdf-adc.yaml
Filename follows compatible, so st,stm32mp23-mdf
> @@ -0,0 +1,383 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/st,stm32-mdf-adc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: STMicroelectronics STM32 Multi-function Digital Filter (MDF) ADC
> +
> +maintainers:
> + - Olivier Moysan <olivier.moysan at foss.st.com>
> +
> +description: |
> + STM32 MDF ADC is a sigma delta analog-to-digital converter dedicated to
> + interface external sigma delta modulators to STM32 micro controllers.
> +
> +properties:
> + compatible:
> + enum:
> + - st,stm32mp25-mdf
> + - st,stm32mp23-mdf
Why reversed order?
> + ranges: true
> +
> + clock-ranges: true
Do you need it here?
> +
> + resets:
> + maxItems: 1
> +
> + reset-names:
> + items:
> + - const: mdf
Drop
> +
> + access-controllers:
> + $ref: /schemas/types.yaml#/definitions/phandle-array
> + description: |
> + Phandle to the rifsc device to check access right.
Look at other code how this is done. Don't come with own stuff.
> +
> + power-domains:
> + maxItems: 1
> +
> + st,interleave:
> + description: |
> + List of phandles of interleaved filters. The indexes of interleaved filters must be
> + consecutives starting from 0 (i.e in range [0..N]). The samples from interleaved filters
> + are muxed in a single channel and retrieved through the device associated to the filter 0.
> + The filters 1..N have to be enabled, but inherit their configuration from filter 0.
> + $ref: /schemas/types.yaml#/definitions/phandle-array
> +
> +required:
> + - compatible
> + - reg
> + - ranges
> + - clocks
> + - clock-names
> + - clock-ranges
> + - "#address-cells"
> + - "#size-cells"
> +
> +additionalProperties: false
> +
> +patternProperties:
And this has odd order. Please look at example-schema.
> + "^sitf@[0-9]+$":
> + type: object
> + description: Serial interface child node
> +
> + properties:
> + compatible:
> + enum:
> + - st,stm32mp25-sitf-mdf
> +
> + reg:
> + description: Specify the SITF serial interface instance
> + maxItems: 1
> +
> + clocks:
> + description: |
> + Serial interface clock (optional depending on interface mode)
> + maxItems: 1
> +
> + st,sitf-mode:
> + description: |
> + Select serial interface protocol
> + - spi: SPI mode
> + - lf_spi: low frequency SPI mode for low power applications
> + $ref: /schemas/types.yaml#/definitions/string
> + enum:
> + - spi
> + - lf_spi
> +
> + required:
> + - reg
> + - st,sitf-mode
> +
> + additionalProperties: false
> +
> + "^filter@[0-9]+$":
> + type: object
> + description: Digital filter path child node
> +
> + properties:
> + compatible:
> + enum:
> + - st,stm32mp25-mdf-dmic
> + - st,stm32mp25-mdf-adc
> +
> + reg:
> + description: Specify the MDF filter instance
> + maxItems: 1
> +
> + interrupts:
> + maxItems: 1
> +
> + clocks:
> + minItems: 1
Heh? so here min? Is there any logic in your choices of code style?
> + description: Internal clock used for MDF digital processing and control blocks.
> +
> + clock-names:
> + items:
> + - const: ker_ck
> +
> + dmas:
> + maxItems: 1
> +
> + dma-names:
> + items:
> + - const: rx
> +
> + "#io-channel-cells":
> + const: 1
> +
> + '#address-cells':
> + const: 1
> +
> + '#size-cells':
> + const: 0
> +
> + st,cic-mode:
> + description: |
> + Cascaded-integrator-comb (CIC) filter configuration
> + - 0: MCIC & ACIC filters in FastSinc mode
> + - [1-3]: MCIC & ACIC filters in Sinc mode order 1 to 3
> + - [4-5]: Single CIC filter in Sinc mode order 4 to 5
> + For audio purpose it is recommended to use CIC Sinc4 or Sinc5
> + This property is mandatory for filter 0 or filters not used in interleave mode.
> + $ref: /schemas/types.yaml#/definitions/uint32
> + minimum: 0
> + maximum: 5
> +
> + st,delay:
> + description: Filter delay in samples
> + $ref: /schemas/types.yaml#/definitions/uint32
> + maximum: 127
> +
> + st,rs-filter-bypass:
> + description: Bypass RSFLT reshaping filter.
> + $ref: /schemas/types.yaml#/definitions/flag
> +
> + st,hpf-filter-cutoff-bp:
> + description: |
> + High Pass Filter (HPF) cut-off frequency expressed as a fraction of the PCM sampling rate.
> + Cut-off frequency = st,hpf-filter-cutoff-bp x Fpcm / 10000.
> + If this property is not defined the HPF is disabled.
> + enum: [625, 1250, 2500, 9500]
> +
> + st,sync:
> + description:
> + Synchronize to another filter.
> + Must contain the phandle of the filter providing the synchronization.
> + allOf:
> + - $ref: /schemas/types.yaml#/definitions/phandle-array
> + - maxItems: 1
> +
> + st,sitf:
> + $ref: /schemas/types.yaml#/definitions/phandle-array
> + items:
> + - items:
> + - description: Phandle of the serial interface connected to the digital filter
> + - description: |
> + The phandle's argument selects the bitstream on the falling or rising edge
> + of the serial interface clock:
> + - 0: rising edge
> + - 1: falling edge
> + enum: [0, 1]
> + default: 0
> + description:
> + Should be phandle/bitstream pair.
> +
> + required:
> + - compatible
> + - reg
> + - interrupts
> + - dmas
> + - dma-names
> + - "#io-channel-cells"
> + - "#address-cells"
> + - "#size-cells"
> + - st,sitf
> +
> + unevaluatedProperties: false
> +
> + patternProperties:
> + "^channel@([0-7])$":
> + type: object
> + $ref: adc.yaml
> + description: Represents the external channel which is connected to the MDF.
> +
> + properties:
> + reg:
> + maximum: 7
> +
> + io-backends:
> + description:
> + Used to pipe external sigma delta modulator or internal ADC backend to MDF
> + channel.
> + maxItems: 1
> +
> + required:
> + - reg
> +
> + unevaluatedProperties: false
> +
> + allOf:
> + - if:
> + properties:
> + compatible:
> + contains:
> + const: st,stm32mp25-mdf-adc
> +
> + then:
> + patternProperties:
> + "^channel@[0-7]$":
> + required:
> + - io-backends
> +
> + - if:
> + properties:
> + compatible:
> + contains:
> + const: st,stm32mp25-mdf-dmic
> +
> + then:
> + patternProperties:
> + "^mdf-dai+$":
This makes no sense. Why is this a pattern and why mdf-daiiiii is
correct name?
Not mentioning that your are not supposed to define properties in if
block (do you see any code like that?). Mixing addressable and
non-addressable children is another odd thing.
This entire schema is quite chaotic and overcomplicated.
> + type: object
> + description: child node
> +
> + properties:
> + compatible:
> + enum:
> + - st,stm32mp25-mdf-dai
> +
> + "#sound-dai-cells":
> + const: 0
> +
> + io-channels:
> + description:
> + From common IIO binding. Used to pipe external sigma delta
> + modulator or internal ADC output to MDF channel.
> +
> + power-domains:
> + maxItems: 1
> +
> + port:
> + $ref: /schemas/sound/audio-graph-port.yaml#
> + unevaluatedProperties: false
> +
> + required:
> + - compatible
> + - "#sound-dai-cells"
> + - io-channels
> +
> + additionalProperties: false
> +
> +examples:
> + - |
> + #include <dt-bindings/clock/st,stm32mp25-rcc.h>
> + #include <dt-bindings/interrupt-controller/arm-gic.h>
> + mdf1: mdf at 504d0000 {
Node names should be generic. See also an explanation and list of
examples (not exhaustive) in DT specification:
https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#generic-names-recommendation
If you cannot find a name matching your device, please check in kernel
sources for similar cases or you can grow the spec (via pull request to
DT spec repo).
And drop unused labels.
> + compatible = "st,stm32mp25-mdf";
> + ranges = <0 0x504d0000 0x1000>;
> + reg = <0x504d0000 0x8>, <0x504d0ff0 0x10>;
Address ranges of 2 and 4 words?
Best regards,
Krzysztof
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