linux-kernel - Re: [PATCH v3 1/4] dt-bindings: backlight: Add max25014 bindingsy

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Message-ID: <5c5cf363-db5c-4d0b-902f-97c6ef06c08f@gocontroll.com>
Date: Mon, 6 Oct 2025 12:02:46 +0200
From: Maud Spierings <maudspierings@...ontroll.com>
To: Frank Li <Frank.li@....com>
Cc: 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>, 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 v3 1/4] dt-bindings: backlight: Add max25014 bindingsy

On 9/12/25 17:22, Frank Li wrote:
> On Fri, Sep 12, 2025 at 08:17:09AM +0200, Maud Spierings wrote:
>> Hi Frank,
>> Thanks for the review.
>>
>> On 9/11/25 17:33, Frank Li wrote:
>>> On Thu, Sep 11, 2025 at 09:53:18AM +0200, Maud Spierings via B4 Relay wrote:
>>>> From: Maud Spierings <maudspierings@...ontroll.com>
>>>>
>>>> The Maxim MAX25014 is a 4-channel automotive grade backlight driver IC
>>>> with integrated boost controller.
>>>>
>>>> Signed-off-by: Maud Spierings <maudspierings@...ontroll.com>
>>>> ---
>>>>    .../bindings/leds/backlight/maxim,max25014.yaml    | 81 ++++++++++++++++++++++
>>>>    MAINTAINERS                                        |  5 ++
>>>>    2 files changed, 86 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..e113a2ad16aa74f982b9c2ea80578aed2d9424fe
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/leds/backlight/maxim,max25014.yaml
>>>> @@ -0,0 +1,81 @@
>>>> +# 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
>>>> +    default: 11
>>>> +    description:
>>>> +      Value of the ISET register field. This controls the current scale of the
>>>> +      outputs, a higher number means more current.
>>>
>>> Use standard unit. Do not use register value directly.
>>
>> It is unfortunately not just a value in Amps, it depends on the hardware
>> design. There is a kind of "default" table with a 49.9K resistor, but
>> depending on that resistor the current is different.
> 
> You should calculate in your driver. if 49.9K is dependence, you should
> add xxx_ohm at dts.

I've tried to find the logic behind the Riref resistor and its 
values/effects, but there is no formula for it, there are example values 
for 49.9k and 40.2k, besides that all that is stated that the minimum 
allowed value is 27.5k and the maximum value is 83.5k.

Not sure how to continue after that, I cannot verify/approximate any 
relation with only two data points.
Kind regards,
Maud