linux-kernel - Re: [PATCH v5 1/7] dt-bindings: connector: Add mikrobus-connector

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Date: Thu, 27 Jun 2024 22:59:46 +0530
From: Ayush Singh <ayush@...gleboard.org>
To: Michael Walle <mwalle@...nel.org>, Mark Brown <broonie@...nel.org>,
 Vaishnav M A <vaishnav@...gleboard.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Derek Kiernan <derek.kiernan@....com>,
 Dragan Cvetic <dragan.cvetic@....com>, Arnd Bergmann <arnd@...db.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Nishanth Menon <nm@...com>,
 Vignesh Raghavendra <vigneshr@...com>, Tero Kristo <kristo@...nel.org>,
 Andrew Lunn <andrew@...n.ch>, jkridner@...gleboard.org,
 robertcnelson@...gleboard.org
Cc: linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 1/7] dt-bindings: connector: Add mikrobus-connector

On 6/27/24 22:42, Michael Walle wrote:

> Hi,
>
> Could you give us a DT snippet of how this should look like with a
> board?
>
> On Thu Jun 27, 2024 at 6:26 PM CEST, Ayush Singh wrote:
>> +  board:
>> +    description: board attached to mikrobus connector
>> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> Shouldn't this be a subnode of the connector?
>
> i.e.
>
> connector {
> 	compatible = "mikrobus-connector";
>
> 	// phandles to the parent controllers
>
> 	spi {
> 		temp-sensor@0 {
> 			compatible = "maxim,max31855k";
> 			reg = <0>;
> 		};
> 	};
>
> 	i2c {
> 		..
> 	};
> };
>
> I don't think you can introduce a new
>    compatible = "maxim,max31855k", "mikrobus,spi";
> if there is already a binding for "maxim,max31855k". But I might be
> wrong. Why is this compatible needed at all?

So I did consider the design you just proposed, but I was not able to 
solve a few issues.

1. How to deal with say 2 mikrobus connectors in a single system?

My goal is to have only 1 overlay required for the board config at most. 
Ideally, I would actually like to add the dt for most mikroBUS boards to 
upstream and thus only the following overlay would be required:

```

&connector0 {

     board = <&temp-board>;

};

```

The problem with making it children is that each connector will require 
seperate overlays for board configs.

Additionally, there are boards with 1 wire eeprom available which can 
theselves store the overlay. In the current setup it will look as follows:

```

&mikrobus_board {

     thermo-sensor {

         ...

     };

};

```

Which is completely independent of the connector. If the same can be 
achieved with child-node as well, then I am open to doing that.

>
> Also, the mikrobus-connector driver could translate the chipselects.
>
> -michael

Yes, so it is currently doing that. Translating chip select name to the 
actual number. I am doing it the name way since some boards might use 
pins other than CS as chipselect and not all connectors will allow all 
pins to be used as chipselect.

Ayush Singh