linux-kernel - Re: [PATCH v2 2/4] dt-bindings: auxdisplay: Add bindings for generic 7 segment LED

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Message-ID: <34b89a56-ab43-4d44-86f3-604e5be29db3@alliedtelesis.co.nz>
Date: Wed, 28 Feb 2024 01:53:08 +0000
From: Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To: Andy Shevchenko <andy.shevchenko@...il.com>
CC: "andy@...nel.org" <andy@...nel.org>, "geert@...ux-m68k.org"
	<geert@...ux-m68k.org>, "robh+dt@...nel.org" <robh+dt@...nel.org>,
	"krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>, "andrew@...n.ch"
	<andrew@...n.ch>, "gregory.clement@...tlin.com"
	<gregory.clement@...tlin.com>, "sebastian.hesselbarth@...il.com"
	<sebastian.hesselbarth@...il.com>, "ojeda@...nel.org" <ojeda@...nel.org>,
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	"lee@...nel.org" <lee@...nel.org>, "pavel@....cz" <pavel@....cz>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
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	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/4] dt-bindings: auxdisplay: Add bindings for generic
 7 segment LED

On 28/02/24 13:03, Andy Shevchenko wrote:
> On Tue, Feb 27, 2024 at 11:22 PM Chris Packham
> <chris.packham@...iedtelesis.co.nz> wrote:
>
> ...
>
>> +  segment-gpios:
>> +    description:
>> +      An array of GPIOs one per segment.
> This is a vague description. Please explain the order (e.g., LSB =
> 'a', MSB = 'g'), use of DP (optional?), etc.
>
>> +    minItems: 7
> maxItems?
>
> ...

I plan on saying maxItems: 7 (more discussion below)

>
>> +    led-7seg {
> Probably it should be more human readable. DT people might suggest
> something better.
>
>> +        compatible = "generic-gpio-7seg";
>> +        segment-gpios = <&gpio 0 GPIO_ACTIVE_LOW
>> +                         &gpio 1 GPIO_ACTIVE_LOW
>> +                         &gpio 2 GPIO_ACTIVE_LOW
>> +                         &gpio 3 GPIO_ACTIVE_LOW
>> +                         &gpio 4 GPIO_ACTIVE_LOW
>> +                         &gpio 5 GPIO_ACTIVE_LOW
>> +                         &gpio 6 GPIO_ACTIVE_LOW>;
> Dunno how to handle DP. Either we always expect it to be here (as
> placeholder) or with additional property.

My current plan was to ignore it. As you see it my later patch I'm 
(ab)using DP as a discrete gpio-led with a different function.

We could either a separate dp-gpios property or set maxItems to 8. Right 
now the driver won't do anything with either option.To actually do 
something in the linedisp driver we'd need to have a new character map 
that includes the extra LED.

>> +    };