linux-kernel - Re: [PATCH v2 1/4] dt-bindings: backlight: Add max25014 bindings

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Message-ID: <a1115bc7-225f-438c-8ae9-c616f42747d7@gocontroll.com>
Date: Wed, 20 Aug 2025 07:19:46 +0200
From: Maud Spierings <maudspierings@...ontroll.com>
To: Rob Herring <robh@...nel.org>
Cc: Lee Jones <lee@...nel.org>, Daniel Thompson <danielt@...nel.org>,
 Jingoo Han <jingoohan1@...il.com>, Pavel Machek <pavel@...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>, 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 v2 1/4] dt-bindings: backlight: Add max25014 bindings

On 8/19/25 21:50, Rob Herring wrote:
> On Tue, Aug 19, 2025 at 12:58:59PM +0200, Maud Spierings wrote:
>> The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
>> with intgrated boost controller.
>>
>> Signed-off-by: Maud Spierings <maudspierings@...ontroll.com>
>> ---
>>   .../bindings/leds/backlight/maxim,max25014.yaml    | 79 ++++++++++++++++++++++
>>   MAINTAINERS                                        |  5 ++
>>   2 files changed, 84 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 0000000000000000000000000000000000000000..30b591152fa31d5e43243cac44c72028b05b5f8a
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
>> @@ -0,0 +1,79 @@
>> +# 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>
>> +
>> +allOf:
>> +  - $ref: common.yaml#
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - maxim,max25014
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  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

done
>> +    default: 11
>> +    description:
>> +      Value of the ISET register field (0-15).
> 
> Perhaps a little on what this controls?

done, for now, it controls the current scale of the backlight, higher 
number = more current. But I will put it in the description in v3

>> +
>> +  maxim,strings:
>> +    $ref: /schemas/types.yaml#/definitions/uint32-array
>> +    description:
>> +      A 4-bit bitfield that describes which led strings to turn on.
>> +    minItems: 4
>> +    maxItems: 4
> 
>         items:
>           maximum: 1
> 
> But why not just an 8-bit value 0x0-0xF?

That is possible too, the logic is inverted in the actual chip, a bit 
set means the string is turned off, but that can be solved with a 
bitwise not. This just felt like a natural way to read/edit it, an 8-bit 
value you have to first translate the bits into a hex value which isn't 
very clear about what it is actually doing.

Is it possible to to 0b0111 notation in a devicetree? That would make it 
better at least.

>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - maxim,strings
>> +
>> +unevaluatedProperties: false
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/gpio/gpio.h>
>> +    #include <dt-bindings/interrupt-controller/irq.h>
>> +
>> +    i2c {
>> +        #address-cells = <1>;
>> +        #size-cells = <0>;
>> +
>> +        backlight: backlight@6f {
> 
> Drop unused labels.

oops dropped

>> +            reg = <0x6f>;
>> +            compatible = "maxim,max25014";
> 
> compatible is always first.

Messed that up in the dtsos too, fixed everywhere in v3

>> +            default-brightness = <50>;
>> +            enable-gpios = <&gpio1 4 GPIO_ACTIVE_HIGH>;
>> +            interrupt-parent = <&gpio1>;
>> +            interrupts = <2 IRQ_TYPE_EDGE_FALLING>;
>> +            pinctrl-names = "default";
>> +            pinctrl-0 = <&pinctrl_backlight>;
> 
> Generally we don't put pinctrl properties in examples as they are always
> allowed.

dropped

>> +            power-supply = <&reg_backlight>;
>> +            pwms = <&pwm1>;
>> +            maxim,iset = <7>;
>> +            maxim,strings = <1 1 1 1>;
>> +        };
>> +    };
>> +
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index e81d5f9fbd16cc384356804390d65652bbb9e3f6..11c73d2e37fac22aea852152746236c1472f41b8 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -14972,6 +14972,11 @@ 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
>>
>> -- 
>> 2.50.1
>>

Thanks for your review!
Kind regards,
Maud