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

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Message-ID: <14c04d1d-f42f-4ac9-a887-ed37cedb4913@kernel.org>
Date: Wed, 28 Jan 2026 11:14:21 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: tessolveupstream@...il.com, 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 27/01/2026 13:46, tessolveupstream@...il.com wrote:
> 
> 
> 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.


You have entire commit msg to explain the hardware and explain WHY you
are doing this. In a concise and readable way. I will not be going
through 2 different email threads with 20 messages to figure that out.

Best regards,
Krzysztof