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

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 09/01/2023 17:52, Lee Jones wrote:
> 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@gmail.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@gmail.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?

Yeah.

> 
>>>>> +        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?

For this device, because it has only tuples of three.

> 
>>>>> +          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?

No, better to have full paths, so automated tools can validate them. If
we ever decide to drop it, we can also make a easier search&replace for
the pattern starting with include/.

> 
>>>>> +          <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?

For light emitting devices, RGB seems to be used for so long, that I
don't expect more permutations (e.g. CMY). On the other hand, someone
might create LED strip with whatever colors, so maybe indeed better to
allow any variations as in array.

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


Best regards,
Krzysztof