linux-kernel - Re: [PATCH v2 1/2] dt-bindings: backlight: gpio-backlight: allow multiple GPIOs

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Message-ID: <54d156ba-e177-4059-a808-2505983b4e2e@gmail.com>
Date: Fri, 23 Jan 2026 16:41:24 +0530
From: tessolveupstream@...il.com
To: Krzysztof Kozlowski <krzk@...nel.org>, lee@...nel.org,
 danielt@...nel.org, jingoohan1@...il.com
Cc: deller@....de, pavel@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, dri-devel@...ts.freedesktop.org,
 linux-fbdev@...r.kernel.org, linux-leds@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: backlight: gpio-backlight: allow
 multiple GPIOs



On 20-01-2026 20:01, Krzysztof Kozlowski wrote:
> On 20/01/2026 13:50, Sudarshan Shetty wrote:
>> Update the gpio-backlight binding to support configurations that require
>> more than one GPIO for enabling/disabling the backlight.
> 
> 
> Why? Which devices need it? How a backlight would have three enable
> GPIOs? I really do not believe, so you need to write proper hardware
> justification.
>

To clarify our hardware setup: 
the panel requires one GPIO for the backlight enable signal, and it 
also has a PWM input. Since the QCS615 does not provide a PWM controller 
for this use case, the PWM input is connected to a GPIO that is driven 
high to provide a constant 100% duty cycle, as explained in the link 
below.
https://lore.kernel.org/all/20251028061636.724667-1-tessolveupstream@gmail.com/T/#m93ca4e5c7bf055715ed13316d91f0cd544244cf5
 
>>
>> Signed-off-by: Sudarshan Shetty <tessolveupstream@...il.com>
>> ---
>>  .../leds/backlight/gpio-backlight.yaml        | 24 +++++++++++++++++--
>>  1 file changed, 22 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml
>> index 584030b6b0b9..4e4a856cbcd7 100644
>> --- a/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml
>> +++ b/Documentation/devicetree/bindings/leds/backlight/gpio-backlight.yaml
>> @@ -16,8 +16,18 @@ properties:
>>      const: gpio-backlight
>>  
>>    gpios:
>> -    description: The gpio that is used for enabling/disabling the backlight.
>> -    maxItems: 1
>> +    description: |
>> +      The gpio that is used for enabling/disabling the backlight.
>> +      Multiple GPIOs can be specified for panels that require several
>> +      enable signals. All GPIOs are controlled together.
>> +    type: array
> 
> There is no such syntax in the bindings, from where did you get it? Type
> is already defined.
> 
> items:
>   minItems: 1
>   maxItems: 3
> 
> 
>> +    minItems: 1
>> +    items:
>> +      type: array
>> +      minItems: 3
>> +      maxItems: 3
>> +      items:
>> +        type: integer
> 
> All this is some odd stuff - just to be clear, don't send us LLM output.
> I don't want to waste my time to review microslop.
> 
> Was it done with help of Microslop?
>

I understand now that the schema changes I proposed were not correct, 
and I will address this in the next patch series. My intention was to 
check whether the gpio-backlight binding could support more than one 
enable-type GPIO. 
Could you please advise what would be an appropriate maximum number of 
GPIOs for gpio-backlight in such a scenario? For example, would allowing 
2 GPIOs be acceptable, or should this case be handled in a different way?
 
> Best regards,
> Krzysztof