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

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Message-ID: <5f78fbe8-288d-4b0a-af57-e834bd1186ba@gmail.com>
Date: Tue, 27 Jan 2026 18:16:36 +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 23-01-2026 16:41, tessolveupstream@...il.com wrote:
> 
> 
> 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?
> 

In line with Daniel’s suggestion, I am planning to adopt a fixed upper 
limit for the number of backlight GPIOs. The current hardware only 
requires two GPIOs, so the maxItems can be set to 2.

If future platforms or customers require support for a higher number 
of GPIOs, this limit can be increased and the driver can be 
updated accordingly.

Kindly advise if this solution aligns with your expectations, or if 
you prefer an alternative maximum value.
 
>> Best regards,
>> Krzysztof
>