linux-kernel - Re: [PATCH 2/8] dt-bindings: connector: Add MikorBUS connector

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Message-ID: <45b1894b-0a15-4efc-95a0-596aa6728fd7@beagleboard.org>
Date: Wed, 11 Sep 2024 23:30:01 +0530
From: Ayush Singh <ayush@...gleboard.org>
To: Rob Herring <robh@...nel.org>
Cc: fabien.parent@...aro.org, d-gole@...com, lorforlinux@...gleboard.org,
 jkridner@...gleboard.org, robertcnelson@...gleboard.org,
 Andrew Davis <afd@...com>, Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, 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>,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/8] dt-bindings: connector: Add MikorBUS connector

On 9/11/24 22:56, Rob Herring wrote:

> On Wed, Sep 11, 2024 at 07:57:19PM +0530, Ayush Singh wrote:
>> Add DT bindings for mikroBUS interface. MikroBUS [0] is an open standard
>> developed by MikroElektronika for connecting add-on boards to
>> microcontrollers or microprocessors.
> Typo in the subject...
>
> Isn't this v6? Where's the revision history?

Well, at this point, it almost has nothing in common with [0] (the 
previous patch series was about making mikroBUS a Linux bus) and is more 
of a continuation of [1]. So I thought it would be better to treat it as 
a new patch series.

>> MikroBUS connector node will optionally act as nexus nodes for routing
>> GPIOs and PWM.
>>
>> For GPIOs, the following pin numbering should be followed:
>>
>>    0: PWM
>>    1: INT
>>    2: RX
>>    3: TX
>>    4: SCL
>>    5: SDA
>>    6: MOSI
>>    7: MISO
>>    8: SCK
>>    9: CS
>>    10: RST
>>    11: AN
>>
>> For PWM, the PWM pin should be on channel 0.
>>
>> I am not quite sure how to deal with the nexus node properties
>> (#gpio-cells, gpio-map, gpio-map-mask, gpio-map-pass-thru) since they
>> seem to conflict with upstream gpio schema (gpio-controller is a
>> dependency of #gpio-cells).
>>
>> [0]: https://www.mikroe.com/
>>
>> Signed-off-by: Ayush Singh <ayush@...gleboard.org>
>> ---
>>   .../bindings/connector/mikrobus-connector.yaml     | 40 ++++++++++++++++++++++
>>   MAINTAINERS                                        |  5 +++
>>   2 files changed, 45 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/connector/mikrobus-connector.yaml b/Documentation/devicetree/bindings/connector/mikrobus-connector.yaml
>> new file mode 100644
>> index 000000000000..603e4627076c
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/connector/mikrobus-connector.yaml
>> @@ -0,0 +1,40 @@
>> +# SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
>> +#
>> +# Copyright (c) Ayush Singh <ayush@...gleboard.org>
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/connector/mikrobus-connector.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: mikroBUS add-on board socket
>> +
>> +maintainers:
>> +  - Ayush Singh <ayush@...gleboard.org>
>> +
>> +properties:
>> +  compatible:
>> +    const: mikrobus-connector
>> +
>> +required:
>> +  - compatible
>> +
>> +additionalProperties: true
> Cannot be true. You're schema must be complete. I don't understand what
> happened to everything else in the binding.


So the current dtschema makes `gpio-controller` dependency of 
`#gpio-cells` which should not hold true for nexus node [2]. I also 
wanted to understand if the nexus node schema should go in upstream 
dtschema or be in kernel tree.

I will try to figure out how nexus node properties should look by taking 
interrupt nexus node bindings as a starting point.


[0]: 
https://lore.kernel.org/linux-arm-kernel/20240627-mikrobus-scratch-spi-v5-0-9e6c148bf5f0@beagleboard.org/

[1]: 
https://lore.kernel.org/linux-arm-kernel/20240702164403.29067-1-afd@ti.com/

[2]: 
https://devicetree-specification.readthedocs.io/en/v0.3/devicetree-basics.html#nexus-nodes-and-specifier-mapping


Ayush Singh