linux-kernel - Re: [PATCH v6 2/2] dt-bindings: power: supply: add support for MAX77759 fuel gauge

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Message-ID: <a55d7e6e6d9515293ca735f25ffd5c925a6ec617.camel@linaro.org>
Date: Thu, 18 Sep 2025 14:02:55 +0100
From: André Draszik <andre.draszik@...aro.org>
To: Thomas Antoine <t.antoine@...ouvain.be>, Conor Dooley <conor@...nel.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
  Conor Dooley <conor+dt@...nel.org>, Sebastian Reichel <sre@...nel.org>,
 Peter Griffin	 <peter.griffin@...aro.org>, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v6 2/2] dt-bindings: power: supply: add support for
 MAX77759 fuel gauge

Hi,

On Thu, 2025-09-18 at 14:36 +0200, Thomas Antoine wrote:
> Hello,
> 
> 
> On 9/15/25 7:31 PM, Conor Dooley wrote:
> > On Mon, Sep 15, 2025 at 12:14:11PM +0200, Thomas Antoine via B4 Relay wrote:
> > > From: Thomas Antoine <t.antoine@...ouvain.be>
> > > 
> > > The Maxim MAX77759 is a companion PMIC for USB Type-C. It contains
> > > Battery Charger, Fuel Gauge, temperature sensors, USB Type-C Port
> > > Controller (TCPC), NVMEM, and additional GPIO interfaces
> > > 
> > > Use max77759-fg compatible to avoid conflict with drivers for other
> > > functions.
> > > 
> > > The battery node is used to pass the REPCAP and ICHGTERM values
> > > needed for the initialization of the fuel gauge.
> > > 
> > > The nvmem cells are used to get initialization values and to backup
> > > the learning and the number of cycles. It should work out of the box
> > > with gs101-oriole and gs101-raven which were previously running
> > > Android.
> > > 
> > > Signed-off-by: Thomas Antoine <t.antoine@...ouvain.be>
> > > ---
> > >  .../bindings/power/supply/maxim,max77759.yaml      | 78 ++++++++++++++++++++++
> > >  1 file changed, 78 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/power/supply/maxim,max77759.yaml
> > > b/Documentation/devicetree/bindings/power/supply/maxim,max77759.yaml
> > > new file mode 100644
> > > index 0000000000000000000000000000000000000000..4d45739fcaf26273ec57b60049d6d0421df38efb
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/power/supply/maxim,max77759.yaml
> > > @@ -0,0 +1,78 @@
> > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/power/supply/maxim,max77759.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Maxim Integrated MAX77759 fuel gauge
> > > +
> > > +maintainers:
> > > +  - Thomas Antoine <t.antoine@...ouvain.be>
> > > +
> > > +allOf:
> > > +  - $ref: power-supply.yaml#
> > > +
> > > +properties:
> > > +  compatible:
> > > +    const: maxim,max77759-fg
> > 
> > Compatible doesn't match the filename, why?
> > I assume the "fg" is fuel-gauge, but can this device be anything else?
> 
> The max77759 is a multifunction chip.
> The following compatibles are already used for some of those functions:
> - maxim,max77759 (for the pmic)
> - maxim,max77759-gpio
> - maxim,max77759-nvmem
> - maxim,max77759-tcpci
> 
> The fuel gauge functionality that is added with this patch is very similar
> to the functionality of the max1720x which is why the filename was chosen
> to fit other maxim fuel gauge chips pattern.
> 
> Maybe it would be better to use the maxim,max77759-battery compatible to
> match the filename? It would also fit with the already existing
> maxim,max77705-battery and maxim,max77849-battery compatibles.

It also has a (battery) charger, a -battery compatible could be misleading.
The datasheet refers to these subblocks as FG (for fuelgauge) and CHARGER.
I'd suggest keeping those terms.

Additionally, the FG block can also measure temperature and battery ID. For
those, a combination of (top-level) PMIC and FG registers are needed
unfortunately. Which means that the FG should probably be an MFD child
device, even though the FG itself doesn't depend on the top-level. Otherwise
it'd be hard to access the top-level PMIC register.


Cheers,
Andre'