Re: [PATCH v3 7/8] mikrobus: Add mikrobus driver

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Ayush Singh <ayushdevel1325@gmail.com>
Cc: 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 7/8] mikrobus: Add mikrobus driver
Date: Fri, 15 Mar 2024 19:32:57 +0000	[thread overview]
Message-ID: <ZfSiaT9WltBDY9yD@shell.armlinux.org.uk> (raw)
In-Reply-To: <20240315184908.500352-8-ayushdevel1325@gmail.com>

On Sat, Mar 16, 2024 at 12:19:05AM +0530, Ayush Singh wrote:
> diff --git a/drivers/misc/mikrobus/Kconfig b/drivers/misc/mikrobus/Kconfig
> new file mode 100644
> index 000000000000..f0770006b4fe
> --- /dev/null
> +++ b/drivers/misc/mikrobus/Kconfig
> @@ -0,0 +1,19 @@
> +menuconfig MIKROBUS
> +	tristate "Module for instantiating devices on mikroBUS ports"
> +	depends on GPIOLIB
> +	depends on W1
> +	depends on W1_MASTER_GPIO
> +	help
> +	  This option enables the mikroBUS driver. mikroBUS is an add-on
> +	  board socket standard that offers maximum expandability with
> +	  the smallest number of pins. The mikroBUS driver instantiates
> +	  devices on a mikroBUS port described by identifying data present
> +	  in an add-on board resident EEPROM, more details on the mikroBUS
> +	  driver support and discussion can be found in this eLinux wiki :
> +	  elinux.org/Mikrobus

I think this is a fallacy. I have boards that support Mikrobus - some of
the SolidRun products do. I have several Mikrobus "click" boards.

This help text seems to imply that Mikrobus click boards include an
EEPROM that identify them, hence you make the support for mikroBUS
depend on it. No, this is not the case - the click boards do not
contain a 1-wire EEPROM.

Please fetch a copy of the official Mikrobus specification which is
available here:

https://download.mikroe.com/documents/standards/mikrobus/mikrobus-standard-specification-v200.pdf

and rather than creating something that is implementation specific but
appears to be generic, create something that is generic with
implementation specific extensions.

You'll find if you search that document, no mention is made of an
"eprom". "identification" is also not found. "one wire", "onewire",
"1-wire", "1wire" are also not found.

What I'm concerned about is if we create this "Mikrobus" subsystem
which appears to be dependent on one-wire EEPROMs somewhere in the
system, and then end up with a load of drivers for various mikroBUS
boards, what about cases where there is no one-wire EEPROM?

-- 
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