Re: [PATCH v3 1/8] dt-bindings: misc: Add mikrobus-connector

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Ayush Singh <ayushdevel1325@gmail.com>,
	linux-kernel@vger.kernel.org, jkridner@beagleboard.org,
	robertcnelson@beagleboard.org,
	Vaishnav M A <vaishnav@beagleboard.org>,
	Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>, Nishanth Menon <nm@ti.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Tero Kristo <kristo@kernel.org>,
	Derek Kiernan <derek.kiernan@amd.com>,
	Dragan Cvetic <dragan.cvetic@amd.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Jiri Slaby <jirislaby@kernel.org>,
	Johan Hovold <johan@kernel.org>, Alex Elder <elder@kernel.org>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-spi@vger.kernel.org, linux-serial@vger.kernel.org,
	greybus-dev@lists.linaro.org
Subject: Re: [PATCH v3 1/8] dt-bindings: misc: Add mikrobus-connector
Date: Fri, 15 Mar 2024 20:20:08 +0000	[thread overview]
Message-ID: <ZfSteEmeQX5IUJnU@shell.armlinux.org.uk> (raw)
In-Reply-To: <314a88e0-19cd-4b95-9cf3-aef1c7579eec@linaro.org>

On Fri, Mar 15, 2024 at 09:09:11PM +0100, Krzysztof Kozlowski wrote:
> > +properties:
> > +  compatible:
> > +    const: mikrobus-connector
> 
> Hm, why do you create binding for the connector, not for some sort of
> controller? Please provide some rationale for this in commit msg.

I think you have a distorted view. I refer you to the Mikroe mikroBUS
specification - it's _just_ a connector which provides a fairly
standardised purpose for each pin and the electrical specifications.
For example of the pins: power, UART, SPIs, I2C, PWM, and analogue
pins.

> > +  pinctrl-names:
> > +    items:
> > +      - const: default
> > +      - const: pwm_default
> > +      - const: pwm_gpio
> > +      - const: uart_default
> > +      - const: uart_gpio
> > +      - const: i2c_default
> > +      - const: i2c_gpio
> > +      - const: spi_default
> > +      - const: spi_gpio
> 
> I fail to see why such choice is related to the connector itself.

This isn't a choice at all. Here's the list of pins:

Analog - AN
Reset - RST
SPI Chip Select - CS
SPI Clock - SCK
SPI Master Input Slave Output - MISO
SPI Master Output Slave Input - MOSI
VCC-3.3V power - +3.3V
Reference Ground - GND
PWM - PWM output
INT - Hardware Interrupt
RX - UART Receive
TX - UART Transmit
SCL - I2C Clock
SDA - I2C Data
+5V - VCC-5V power
GND - Reference Ground

Any data pin can be a GPIO if e.g. a relay board is plugged in, even
if some of the other pins are used for e.g. UART purposes. For example,
a GPS board that provides the GPS data over the UART pins, and the
PPS signal through a different pin.

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