linux-kernel - Re: [PATCH v5 7/7] dts: ti: k3-am625-beagleplay: Add mikroBUS

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Message-Id: <D2AZ0QKTPY3B.1I48GLI90XD0P@kernel.org>
Date: Thu, 27 Jun 2024 19:21:03 +0200
From: "Michael Walle" <mwalle@...nel.org>
To: "Andrew Davis" <afd@...com>, "Ayush Singh" <ayush@...gleboard.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 7/7] dts: ti: k3-am625-beagleplay: Add mikroBUS

On Thu Jun 27, 2024 at 7:07 PM CEST, Andrew Davis wrote:
> > +	mikrobus_boards {
> > +		thermo_click: thermo-click {
> > +			compatible = "maxim,max31855k", "mikrobus-spi";
>
> I might be missing something, but your solution cannot possibly be
> to list every click board that could be connected (all 1500+ of them)
> to every mikroBUS connector on every device's DT file..
>
> Each click board should have a single DTSO overlay file to describe the
> click board, one per click board total. And then that overlay should
> apply cleanly to any device that has a mikroBUS interface.
>
> Which means you have not completely solved the fundamental problem of
> abstracting the mikroBUS connector in DT. Each of these click device child
> nodes has to be under the parent connector node. Which means a phandle
> to the parent node, which is not generically named. For instance
> if my board has 2 connectors, I would have mikrobus0 and mikrobus1,
> the click board's overlay would look like this:
>
> /dts-v1/;
> /plugin/;
>
> &mikrobus0 {
> 	status = "okay";
>
> 	mikrobus_board {
> 		thermo-click {
> 			compatible = "maxim,max31855k", "mikrobus-spi";
> 			spi-max-frequency = <1000000>;
> 			pinctrl-apply = "spi_default";
> 		};
> 	};
> };

If there should only be one DT overlay per click board, how would
you apply that to to different connectors?

> I think this solution is almost there, but once you solve the above
> issue, we could just apply the right overlay for our attached click
> board ahead of time and not need the mikroBUS bus driver at all.

The bus driver would still be needed to do the enumeration of the
children, no? And it could make the chip select translations etc. So
you can use the normal bindings of these devices.

-michael