Message-ID: <20251009-overjoyed-unpopular-54f69e9bd82c@spud>
Date: Thu, 9 Oct 2025 19:21:00 +0100
From: Conor Dooley <conor@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: maudspierings@...ontroll.com, Lee Jones <lee@...nel.org>,
	Daniel Thompson <danielt@...nel.org>,
	Jingoo Han <jingoohan1@...il.com>, Pavel Machek <pavel@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Helge Deller <deller@....de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, dri-devel@...ts.freedesktop.org,
	linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 1/4] dt-bindings: backlight: Add max25014 bindings

On Thu, Oct 09, 2025 at 10:55:42AM -0400, Frank Li wrote:
> On Thu, Oct 09, 2025 at 08:48:25AM +0200, Maud Spierings via B4 Relay wrote:
> > From: Maud Spierings <maudspierings@...ontroll.com>
> 
> Subject needn't double bindings.
> 
> dt-bindings: backlight: Add max25014 support
> 
> >
> > The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
> > with integrated boost controller.
> >
> > In the current implementation the control registers for channel 1,
> > control all channels. So only one led subnode with led-sources is
> > supported right now. If at some point the driver functionality is
> > expanded the bindings can be easily extended with it.
> 
> Need descript hardware, not driver. Need descript full functions even though
> driver have not implement yet.
> 
> >
> > Signed-off-by: Maud Spierings <maudspierings@...ontroll.com>
> > ---
> >  .../bindings/leds/backlight/maxim,max25014.yaml    | 109 +++++++++++++++++++++
> >  MAINTAINERS                                        |   5 +
> >  2 files changed, 114 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml b/Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
> > new file mode 100644
> > index 0000000000000..496520e1374e5
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
> > @@ -0,0 +1,109 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/leds/backlight/maxim,max25014.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Maxim max25014 backlight controller
> > +
> > +maintainers:
> > +  - Maud Spierings <maudspierings@...ontroll.com>
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - maxim,max25014
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  "#address-cells":
> > +    const: 1
> > +
> > +  "#size-cells":
> > +    const: 0
> > +
> > +  enable-gpios:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  power-supply:
> > +    description: Regulator which controls the boost converter input rail.
> > +
> > +  pwms:
> > +    maxItems: 1
> > +
> > +  maxim,iset:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    maximum: 15
> > +    default: 11
> > +    description:
> > +      Value of the ISET register field. This controls the current scale of the
> > +      outputs, a higher number means more current.
> 
> Can't use register value directly, need use standard unit. or percentage
> 
> 100: means max, 0: min.

From that datasheet, it seems like the values here don't neatly map to
currents, because it depends on the value of the iref register. I don't
love percentages here either, too much of a force-fit for me.

If current is used, a property for the reference resistor will be
needed, to compute the register values. That only makes sense to me if
Maxim/Analog provide a formula that can be used to calculate the
appropriate register value, and I did not find one in the datasheet from
my quick skim, only two example current tables.
Sure, those two examples can be reverse-engineered to give a way to
compute it, but can we be sure that the numbers apply across the whole
range of permitted values for the resistor?

I don't like using register values for stuff, but I think it is the most
accurate and least likely to cause problems way of representing this.

Maud, on the language used - its the ISET field in the ISET register, I
think the property should make that clear.

> > +patternProperties:
> > +  "^led@[01]$":

Why does this have [01] if reg has to be zero?

> > +    type: object
> > +    description: Properties for a string of connected LEDs.
> > +    $ref: common.yaml#
> > +
> > +    properties:
> > +      reg:
> > +        const: 0
> > +
> > +      led-sources:
> > +        allOf:
> > +          - minItems: 1
> > +            maxItems: 4
> > +            items:
> > +              minimum: 0
> > +              maximum: 3
> > +            default: [0, 1, 2, 3]
> > +
> > +      default-brightness:
> > +        minimum: 0
> > +        maximum: 100
> > +        default: 50
> > +
> > +    required:
> > +      - reg
> > +
> > +    additionalProperties: false
> 
> there are $ref, should use unevaluatedProperties: false

Not always, looks like they've listed some properties from the file,
which would make addtionalPropeties: false correct if they dont want
the other properties in the file to be used.

> 
> Frank
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/gpio/gpio.h>
> > +    #include <dt-bindings/interrupt-controller/irq.h>
> > +
> > +    i2c {
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        backlight@6f {
> > +            compatible = "maxim,max25014";
> > +            reg = <0x6f>;
> > +            enable-gpios = <&gpio1 4 GPIO_ACTIVE_HIGH>;
> > +            interrupt-parent = <&gpio1>;
> > +            interrupts = <2 IRQ_TYPE_EDGE_FALLING>;
> > +            power-supply = <&reg_backlight>;
> > +            pwms = <&pwm1>;
> > +            maxim,iset = <7>;
> > +
> > +            #address-cells = <1>;
> > +            #size-cells = <0>;
> > +
> > +            led@0 {
> > +                reg = <0>;
> > +                led-sources = <0 1 2 3>;
> > +                default-brightness = <50>;
> > +            };
> > +        };
> > +    };
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 47fbc5e06808f..be5e2515900ce 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -15171,6 +15171,11 @@ F:	Documentation/userspace-api/media/drivers/max2175.rst
> >  F:	drivers/media/i2c/max2175*
> >  F:	include/uapi/linux/max2175.h
> >
> > +MAX25014 BACKLIGHT DRIVER
> > +M:	Maud Spierings <maudspierings@...ontroll.com>
> > +S:	Maintained
> > +F:	Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
> > +
> >  MAX31335 RTC DRIVER
> >  M:	Antoniu Miclaus <antoniu.miclaus@...log.com>
> >  L:	linux-rtc@...r.kernel.org
> >
> > --
> > 2.51.0
> >
> >

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