linux-kernel - Re: [PATCH 2/3] dt-bindings: leds: add dt schema for worldsemi,ws2812b-spi

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Message-ID: <98b72494-3188-76d5-2e24-9dc127a8b31a@linaro.org>
Date:   Tue, 29 Nov 2022 17:54:52 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Chuanhong Guo <gch981213@...il.com>, linux-leds@...r.kernel.org
Cc:     Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Stanislav Jakubek <stano.jakubek@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Johan Hovold <johan+linaro@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Sven Schwermer <sven.schwermer@...ruptive-technologies.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] dt-bindings: leds: add dt schema for
 worldsemi,ws2812b-spi

On 29/11/2022 15:09, Chuanhong Guo wrote:
> This patch adds dt binding schema for WorldSemi WS2812B driven using SPI
> bus.
> 
> Signed-off-by: Chuanhong Guo <gch981213@...il.com>
> ---
>  .../bindings/leds/worldsemi,ws2812b-spi.yaml  | 131 ++++++++++++++++++
>  1 file changed, 131 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/leds/worldsemi,ws2812b-spi.yaml
> 
> diff --git a/Documentation/devicetree/bindings/leds/worldsemi,ws2812b-spi.yaml b/Documentation/devicetree/bindings/leds/worldsemi,ws2812b-spi.yaml
> new file mode 100644
> index 000000000000..8544bde4f261
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/leds/worldsemi,ws2812b-spi.yaml
> @@ -0,0 +1,131 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/leds/worldsemi,ws2812b-spi.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: WS2812B LEDs driven using SPI
> +
> +maintainers:
> +  - Chuanhong Guo <gch981213@...il.com>
> +
> +description: |
> +  WorldSemi WS2812B is a individually addressable LED chip that can be chained
> +  together and controlled individually using a single wire.
> +  This driver simulates the protocol used by this LED chip with SPI bus.

Drop references to Linux driver, unless important for the binding.

> +  Typical setups includes connecting the data pin of the LED chain to MOSI as
> +  the only device or using CS and MOSI with a tri-state voltage-level shifter
> +  for the data pin.
> +  The SPI frequency needs to be 2.105MHz~2.85MHz for the timing to be correct
> +  and the controller needs to send all the bytes continuously.
> +
> +allOf:
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +properties:
> +  compatible:
> +    const: worldsemi,ws2812b-spi

Drop "-spi". Compatibles are not supposed to include bus information.
The same for file name.

> +
> +  reg:
> +    description: The chip-select line on the SPI bus

Drop description, it's obvious.

> +    maxItems: 1
> +
> +  spi-max-frequency:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      Maximum SPI clocking speed of the device in Hz.

No need for ref and description. It comes from spi-peripheral-props.

> +    minimum: 2105000
> +    maximum: 2850000
> +
> +  "#address-cells":
> +    const: 1
> +
> +  "#size-cells":
> +    const: 0
> +
> +patternProperties:
> +  "^multi-led(@[0-9a-f])?$":

Why unit address is optional?

> +    type: object
> +    $ref: leds-class-multicolor.yaml#

    unevaluatedProperties: false

> +
> +    properties:
> +      color-index:
> +        description: |
> +          A 3-item array specifying color of each components in this LED. It
> +          should be one of the LED_COLOR_ID_* prefixed definitions from the
> +          header include/dt-bindings/leds/common.h. Defaults to
> +          <LED_COLOR_ID_GREEN LED_COLOR_ID_RED LED_COLOR_ID_BLUE>
> +          if unspecified.
> +        $ref: /schemas/types.yaml#/definitions/uint32-array
> +        minItems: 3

Drop minItems.... but see comment below:

> +        maxItems: 3

Why this is different than other multi-color LEDs? I would expect here
children with common.yaml.

> +
> +      default-intensity:
> +        description: |
> +          An array of 3 integer specifying the default intensity of each color
> +          components in this LED. <255 255 255> if unspecified.
> +        $ref: /schemas/types.yaml#/definitions/uint32-array
> +        minItems: 3

Drop minItems.... but:

> +        maxItems: 3
> +        items:
> +          minimum: 0
> +          maximum: 255

default: 255

What controls the intensity? Don't you have PWM there?

> +
> +      reg:
> +        description: |
> +          Which LED this node represents. The reg of the first LED on the chain
> +          is 0.

maxItems: 1

> +
> +    required:
> +      - reg
> +      - color
> +      - function
> +
> +required:
> +  - compatible
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/leds/common.h>
> +    spi {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        ws2812b@0 {

Node names should be generic.
https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#generic-names-recommendation

> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +            compatible = "worldsemi,ws2812b-spi";
> +            reg = <0>;

compatible is first property, reg is second.


Best regards,
Krzysztof