linux-kernel - Re: [PATCH v4 2/3] dt-bindings: leds: add worldsemi,ws2812b

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Message-ID: <Y7xGUiWBKIAm9YFA@google.com>
Date:   Mon, 9 Jan 2023 16:52:34 +0000
From:   Lee Jones <lee@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Pavel Machek <pavel@....cz>, Chuanhong Guo <gch981213@...il.com>,
        linux-leds@...r.kernel.org, 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 v4 2/3] dt-bindings: leds: add worldsemi,ws2812b

On Sat, 24 Dec 2022, Krzysztof Kozlowski wrote:

> On 23/12/2022 18:19, Pavel Machek wrote:
> > Hi!
> > 
> >>> Add dt binding schema for WorldSemi WS2812B driven using SPI
> >>> bus.
> >>>
> >>> Signed-off-by: Chuanhong Guo <gch981213@...il.com>
> >>> ---
> >>> Changes since v1:
> >>> remove linux driver reference from description
> >>> remove some obvious descriptions
> >>> fix unit address regex in multi-led property
> >>> drop various minItems
> >>> add maxItems = 1 to reg
> >>> fix node names and property orders in binding example
> >>> drop -spi from compatible string
> >>> add default-brightness
> >>>
> >>> Change since v2:
> >>> drop "this patch" from commit message
> >>> rename leds to led-controller
> >>> drop default-brightness and default-intensity
> >>>
> >>> Change since v3:
> >>> reword commit title
> >>>
> >>>  .../bindings/leds/worldsemi,ws2812b.yaml      | 116 ++++++++++++++++++
> >>>  1 file changed, 116 insertions(+)
> >>>  create mode 100644 Documentation/devicetree/bindings/leds/worldsemi,ws2812b.yaml
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/leds/worldsemi,ws2812b.yaml b/Documentation/devicetree/bindings/leds/worldsemi,ws2812b.yaml
> >>> new file mode 100644
> >>> index 000000000000..548c05ac3d31
> >>> --- /dev/null
> >>> +++ b/Documentation/devicetree/bindings/leds/worldsemi,ws2812b.yaml
> >>> @@ -0,0 +1,116 @@
> >>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> >>> +%YAML 1.2
> >>> +---
> >>> +$id: http://devicetree.org/schemas/leds/worldsemi,ws2812b.yaml#
> >>> +$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 binding describes a chain of WS2812B LEDs connected to the SPI MOSI pin.
> >>> +  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:
> >>> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> >>> +
> >>> +properties:
> >>> +  compatible:
> >>> +    const: worldsemi,ws2812b
> >>> +
> >>> +  reg:
> >>> +    maxItems: 1
> >>> +
> >>> +  spi-max-frequency:
> >>> +    minimum: 2105000
> >>> +    maximum: 2850000
> >>> +
> >>> +  "#address-cells":
> >>> +    const: 1
> >>> +
> >>> +  "#size-cells":
> >>> +    const: 0
> >>> +
> >>> +patternProperties:
> >>> +  "^multi-led@[0-9a-f]+$":
> >>> +    type: object
> >>> +    $ref: leds-class-multicolor.yaml#
> >>> +    unevaluatedProperties: false
> >>> +
> >>> +    properties:
> >>> +      color-index:

Why "index"?

Isn't it just an array of colours rather than an index into something?

> >>> +        description: |
> >>> +          A 3-item array specifying color of each components in this LED. It

Why are you forcing this to 3?

Surely there are multi-colour LEDs containing more or less colours?

> >>> +          should be one of the LED_COLOR_ID_* prefixed definitions from the
> >>> +          header include/dt-bindings/leds/common.h. Defaults to

Isn't "include" a Linuxisum?

> >>> +          <LED_COLOR_ID_GREEN LED_COLOR_ID_RED LED_COLOR_ID_BLUE>
> >>> +          if unspecified.
> >>> +        $ref: /schemas/types.yaml#/definitions/uint32-array
> >>> +        maxItems: 3
> >>
> >> In general I am fine with it, although there is still question for
> >> adding more multi-color defines in binding headers to replace this
> >> property - GRB/RBG/GBR and even more for RGBW.
> >>
> >> Pavel, Lee, any thoughts from your side?
> > 
> > This really needs to mention the name this hardware is known as -- I
> > believe it is NeoPixel.
> 
> We wait here for feedback on colors... The binding is re-implementing
> color, just because of combinations GRB/RBG/GBR, which could be achieved
> with new color defines.

Sure, but where does that end?

How many permutations are there likely to be?

An unlimited array has more of a chance of standing the test of time.

-- 
Lee Jones [李琼斯]