linux-kernel - Re: [PATCH 0/6] mfd: Add support for the LTC4283 Hot Swap Controller

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Message-ID: <20250820200354.GA602656-robh@kernel.org>
Date: Wed, 20 Aug 2025 15:03:54 -0500
From: Rob Herring <robh@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>
Cc: Guenter Roeck <linux@...ck-us.net>, nuno.sa@...log.com,
	linux-hwmon@...r.kernel.org, linux-gpio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, Lee Jones <lee@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jean Delvare <jdelvare@...e.com>, Jonathan Corbet <corbet@....net>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: [PATCH 0/6] mfd: Add support for the LTC4283 Hot Swap Controller

On Thu, Aug 14, 2025 at 03:15:29PM +0100, Nuno Sá wrote:
> On Thu, Aug 14, 2025 at 05:54:26AM -0700, Guenter Roeck wrote:
> > On 8/14/25 03:52, Nuno Sá via B4 Relay wrote:
> > > The LTC4283 device features programmable current limit with foldback and
> > > independently adjustable inrush current to optimize the MOSFET safe
> > > operating area (SOA). The SOA timer limits MOSFET temperature rise for
> > > reliable protection against overstresses.
> > > 
> > > An I2C interface and onboard ADC allow monitoring of board current, voltage,
> > > power, energy, and fault status.
> > > 
> > > It also features 8 pins that can be configured as GPIO devices. But since
> > > the main usage for this device is monitoring, the GPIO part is optional
> > > while the HWMON is being made as required.
> > > 
> > > Also to note that the device has some similarities with the already
> > > supported ltc4282 hwmon driver but it is different enough to be in it's own
> > > driver (apart from being added as MFD). The register map is also fairly
> > > different.
> > > 
> > > Last time (for the ltc4282) I tried to add the gpio bits directly in the
> > > hwmon driver but Guenter did not really liked it and so this time I'm doing
> > > it as MFD.
> > > 
> > Nowadays I suggest that people use auxiliary drivers in such situations.
> 
> I see. But do you have any issue with it being MFD?

I do...

> I'm anyways tempted to the auxiliary device idea. The main usage for
> this device is HWMON and I dunno anyone would use it only as a GPIO
> controller. With the auxiliary device we would only need one bindings file
> and slightly better bindings for the pins functionality.

For this reason. The driver structure influencing the binding design is 
a problem, but I think MFD is more to blame on that.

Rob