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

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Message-ID: <jhtvuwdako2r3pgj6lwxlgb6godnleqezh6kdiswn2mqslqy7w@6p6ixj3hrckq>
Date: Mon, 25 Aug 2025 10:07:52 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Rob Herring <robh@...nel.org>
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 Wed, Aug 20, 2025 at 03:03:54PM -0500, Rob Herring wrote:
> 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.
> 

Alright, it seems we're aligning for auxiliary device on v2.

- Nuno Sá
> Rob