Message-ID: <c127af0d-7e9b-420f-b241-e26ede6b79b7@beagleboard.org>
Date: Fri, 13 Sep 2024 15:53:03 +0530
From: Ayush Singh <ayush@...gleboard.org>
To: Alexander Stein <alexander.stein@...tq-group.com>,
 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>, 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>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/8] Add generic overlay for MikroBUS addon boards


On 9/13/24 15:35, Alexander Stein wrote:
> Hi,
>
> Am Mittwoch, 11. September 2024, 16:27:17 CEST schrieb Ayush Singh:
>> Hello all,
>>
>> This is an attempt to add MikroBUS addon support using the approach
>> described by Grove connector patch series [0].
>>
>> The patch series tests out 2 addon boards + pwm and GPIO on the MikroBUS
>> connector. The boards used are GPS3 Click (for UART) [1] and Weather
>> Click (for I2C) [2]. Additionally, I have tested relative GPIO numbering
>> using devicetree nexus nodes [3].
>>
>> The patch series does not attempt to do any dynamic discovery for 1-wire
>> eeprom MikroBUS addon boards, nor does it provide any sysfs entry for
>> board addition/removal. The connector driver might include them after
>> the basic support is ironed out, but the existing patches for dynamic
>> overlays work fine.
>> [sniip]
> To put it in a more abstract perspective, aren't you "just" defining some
> kind of connector with a fixed layout of pins and features?
> It's not really different to Arduino Shields and Raspberry Pi hats, no?
> Ignoring multi-purpose pins for GPIO or e.g. I2C, this is about matching
> the plugin module's pins to platform-specific on-board peripherals.
>
> Sticking the name to MikroBUS might be misleading, because this is AFAICT
> just a trademark for a specific connector pin layout.
> This concept could be applied for any kind of connector, where e.g.
> the I2C interface is mapped to i2c0 on one platform and to lpi2c5
> on a different platform.
>
> Best regards,
> Alexander


Yes, the only thing specific to mikroBUS in the patches is the connector 
symbols. Theoretically, it is supposed to be usable with any connector. 
MikroBUS is just the connector I am trying to apply the concept to.

I think I came across a bit too mikroBUS specific in the patches here, 
since well that is the connector I am currently trying to support, but 
as the original patches by Andrew [0] explain, this approach was 
proposed to work as a generic way to support such connectors, and even 
do connector stacking.

Trying to use it with MikroBUS shows some limitations we have with the 
current device tree stuff

1. SPI chipselect

2. Nexus nodes need the node to have some kind of existing driver

3. A good place to store the board overlays

4. Stacking needs phandle symbols table support

5. Append property support in devicetree


And of course, I might encounter more limitations as I continue to test 
more boards with it.


[0]: 
https://lore.kernel.org/linux-arm-kernel/20240702164403.29067-1-afd@ti.com/


Ayush Singh

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