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Subject: Re: [PATCH 2/3] dt-bindings: leds: Shiji Lighting APA102C LED driver
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Nicolas Belin <nbelin@baylibre.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-leds@vger.kernel.org, Pavel Machek <pavel@ucw.cz>,
        Dan Murphy <dmurphy@ti.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, Lukas Wunner <lukas@wunner.de>
References: <1582018657-5720-1-git-send-email-nbelin@baylibre.com>
 <1582018657-5720-3-git-send-email-nbelin@baylibre.com>
 <CAMuHMdWPgUKOHyspV3bL_4YKsxgXvEgQqdOzoo-8s8gi_g3rVw@mail.gmail.com>
From:   Jacek Anaszewski <jacek.anaszewski@gmail.com>
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Message-ID: <cb7bbe8a-73dc-8640-7b5d-79a7a3d64e84@gmail.com>
Date:   Thu, 20 Feb 2020 20:41:45 +0100
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Hi Geert,

On 2/20/20 11:30 AM, Geert Uytterhoeven wrote:
> Hi Nicolas,
> 
> CC devicetree, Lukas
> 
> On Tue, Feb 18, 2020 at 10:39 AM Nicolas Belin <nbelin@baylibre.com> wrote:
>> Document Shiji Lighting APA102C LED driver device tree bindings.
>>
>> Signed-off-by: Nicolas Belin <nbelin@baylibre.com>
>> ---
>>  .../devicetree/bindings/leds/leds-apa102c.yaml     | 91 ++++++++++++++++++++++
>>  1 file changed, 91 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/leds/leds-apa102c.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/leds/leds-apa102c.yaml b/Documentation/devicetree/bindings/leds/leds-apa102c.yaml
>> new file mode 100644
>> index 000000000000..24bc2fc19fcb
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/leds/leds-apa102c.yaml
>> @@ -0,0 +1,91 @@
>> +# SPDX-License-Identifier: GPL-2.0
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/leds/leds-apa102c.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: LED driver for Shiji Lighting - APA102C
>> +
>> +maintainers:
>> +  - Nicolas Belin <nbelin@baylibre.com>
>> +
>> +description:
>> +  Each LED is represented as a sub-node of the leds-apa102c device.  Each LED
>> +  is a three color RGB LED with 32 levels brightness adjustment that can be
>> +  cascaded so that multiple LEDs can be set with a single command.
>> +
>> +properties:
>> +  compatible:
>> +    const: shiji,apa102c
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  spi-max-frequency:
>> +    maximum: 1000000
>> +
>> +  "#address-cells":
>> +    const: 1
>> +
>> +  "#size-cells":
>> +    const: 0
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - spi-max-frequency
>> +  - '#address-cells'
>> +  - '#size-cells'
>> +
>> +patternProperties:
>> +  "^led@[0-9]+$":
>> +    type: object
>> +    description: |
>> +      Properties for an array of connected LEDs.
>> +
>> +    properties:
>> +      reg:
>> +        description: |
>> +          This property corresponds to the led index. It has to be between 0
>> +          and the number of managed leds minus 1
>> +        maxItems: 1
>> +
>> +      label:
>> +        description: |
>> +          This property corresponds to the name of the led. If not set,
>> +          the led index will be used to create the led name instead
>> +        maxItems: 1
>> +
>> +      linux,default-trigger: true
>> +
>> +    required:
>> +      - reg
>> +
>> +examples:
>> +  - |
>> +    spi {
>> +        #address-cells = <1>;
>> +        #size-cells = <0>;
>> +
>> +        led-controller@0 {
>> +            compatible = "shiji,apa102c";
>> +            reg = <0>;
>> +            #address-cells = <1>;
>> +            #size-cells = <0>;
>> +            spi-max-frequency = <1000000>;
>> +            led@0 {
>> +                reg = <0>;
>> +                label = "led1";
>> +            };
>> +
>> +            led@1 {
>> +                reg = <1>;
>> +                label = "led2";
>> +            };
>> +
>> +            led@2 {
>> +                reg = <2>;
>> +                label = "led3";
>> +            };
>> +        };
>> +    };
> 
> Perhaps this should use "#daisy-chained-devices" instead of listing all LEDs
> explicitly?
> Or would that cause problems w.r.t. LED labeling?

It would be against common LED bindings.

Besides, this daisy-chain-devices property is not well documented.
I.e. I don't see how it facilitates conveying information on output
ID (here reg is used for that), and as you already mentioned
- LED labeling.

Generally speaking, I don't think it is applicable to the LED subsystem.

> Documentation/devicetree/bindings/common-properties.txt
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 

-- 
Best regards,
Jacek Anaszewski