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

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Date:   Wed, 30 Nov 2022 09:33:08 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     Chuanhong Guo <gch981213@...il.com>, linux-leds@...r.kernel.org,
        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 30/11/2022 01:14, Sebastian Reichel wrote:
>>> +      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
> 
> I would argue, that the default should be 0 (off) instead of 255
> (full power).

Yes.

> 
>> What controls the intensity? Don't you have PWM there?
> 
> WS2812 is a RGB led, which contains a small Microcontroller. The µC
> takes 24 byte intensity data from a serial input and then passes on
> any following bits to the next LED. SPI clk and chip-select are
> ignored (chip-select support can be trivially added though).
> 
> You can find them everywhere nowadays, since they are quite cheap
> (a few cents per LED) and need only one MOSI pin to control hundreds
> of LEDs.

OK. This should be anyway existing property, so default-brightness.

Best regards,
Krzysztof