linux-kernel - Re: [PATCH v4 0/6] Add support for the LTM8054 voltage regulator

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Message-Id: <563331EB-2460-4CF5-87B3-5FE60B18BB70@goldelico.com>
Date: Mon, 24 Nov 2025 16:35:28 +0100
From: "H. Nikolaus Schaller" <hns@...delico.com>
To: Romain Gantois <romain.gantois@...tlin.com>
Cc: Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>,
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 Andy Shevchenko <andriy.shevchenko@...el.com>
Subject: Re: [PATCH v4 0/6] Add support for the LTM8054 voltage regulator

Hi

> Am 24.11.2025 um 16:13 schrieb Romain Gantois <romain.gantois@...tlin.com>:
> 
> Hello Guenter,
> 
> On Monday, 24 November 2025 15:57:41 CET Guenter Roeck wrote:
> > On 11/24/25 06:48, Romain Gantois wrote:
> > > Hello everyone,
> > > 
> > > This is version four of my series which adds initial support of the Linear
> > > Technology LTM8054 voltage regulator. The driver supports a fixed voltage
> > > and a tunable output current limit using a DAC-controlled pin.
> > > 
> > > I'd say that the most unusual part of this series is the usage of the IIO
> > > consumer API in a regulator driver. I think this makes sense here, since
> > > the regulator driver has to access a DAC to read/set the output current
> > > limit.
> > 
> > I don't think that is a valid reason. Literally every driver measuring
> > voltages or current uses a DAC to do it. How else would one convert an
> > analog value into a digital value ?
> 
> Sorry, I don't quite understand your remark. To integrate this voltage 
> regulator component into the Linux regulator abstraction, I'm providing a 
> current limit control function. To provide such a function, the voltage level 
> on a pin has to be controlled. AFAIK, the kernel abstraction used to set 
> precise voltages on lines is an IO channel.

I was curious to learn about this topic and looked into the data sheet:

https://www.analog.com/media/en/technical-documentation/data-sheets/8054fa.pdf

As far as I see the LTM8054 does not even have a programming interface.
So is it reasonable to provide a dedicated driver at all?

The figure on page 20 seems to suggest that there is an external DAC
which drives the regulator. And the regulator drives for example a fan.

So I would think of a driver for the specific DAC and ignore the specific
LTM chip at all.

What could be necessary is if you really want to be able to "regulate"
the current going to Vout, some bridge between regulator API and some
IIO DAC.

And enabling/disabling the regulator by some GPIO can be described in
the DT already through a "regulator-fixed".

But this are just my first thoughts as I have not been following this
topic before. Hope it helps.

BR,
Nikolaus