linux-kernel - Re: [PATCH v7 9/9] misc: add FPC202 dual port controller driver

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Message-ID: <6232449.lOV4Wx5bFT@fw-rgant>
Date: Thu, 20 Feb 2025 13:51:13 +0100
From: Romain Gantois <romain.gantois@...tlin.com>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Romain Gantois <romain.gantois@...tlin.com>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Andi Shyti <andi.shyti@...nel.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>, Mauro Carvalho Chehab <mchehab@...nel.org>,
 Linus Walleij <linus.walleij@...aro.org>,
 Bartosz Golaszewski <brgl@...ev.pl>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Kory Maincent <kory.maincent@...tlin.com>, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-media@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v7 9/9] misc: add FPC202 dual port controller driver

Hello Wolfram,

On jeudi 20 février 2025 13:09:03 heure normale d’Europe centrale Wolfram Sang 
wrote:
> > as this is a i2c_driver, why isn't it in drivers/i2c/ somewhere?  Why
> > misc?
> 
> Because drivers/i2c is only for I2C controllers and this is not a
> controller. Other address translators also reside in their respective
> subsystem, e.g. media for GMSL (de-)serializers. I don't know this chip,
> maybe it has no "respective" subsystem and, thus, misc?

That is correct, this chip acts both as an I2C address translator and as a 
GPIO controller with LED control and prefetch capabilities. It's meant to 
aggregate control signals from multiple SFP cages (or other similar port 
types), which have both I2C and low-speed signals.

Moreover, the chip can be configured to use an SPI master interface instead of 
an I2C one, although this isn't supported in this driver.

Considering all of this, I didn't think that either the I2C subsystem or the 
GPIO subsystem were a good fit for this component, which is why I chose the 
misc subsystem.

Best Regards,

-- 
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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