Re: [PATCH 1/8] dt-bindings: display: panel: novatek,nt36672e: Document the reset GPIO polarity

[Vladimir Zapolskiy <vz@kernel.org>]

On 10/28/26 15:56, Krzysztof Kozlowski wrote:
> On Wed, Oct 28, 2026 at 11:51:44AM +0200, Vladimir Zapolskiy wrote:
>> The reset GPIO of NT36672E panels has been described as active high since
>> the binding was added, also see the example and the QCM6490 IDP board
>> device tree, however actually it serves as the active low signal, also
>> panel-common.yaml expects active low reset GPIOs to be described as such.
>>
>> Document the active high description of the reset GPIO explicitly as
>> the exceptional deviation from the actual signal polarity, any new devices
>> will use it in the same way as the existing ones.
>>
>> Signed-off-by: Vladimir Zapolskiy <vz@kernel.org>
>> ---
>>   .../bindings/display/panel/novatek,nt36672e.yaml         | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/display/panel/novatek,nt36672e.yaml b/Documentation/devicetree/bindings/display/panel/novatek,nt36672e.yaml
>> index dc4672f3d01d..45743376995b 100644
>> --- a/Documentation/devicetree/bindings/display/panel/novatek,nt36672e.yaml
>> +++ b/Documentation/devicetree/bindings/display/panel/novatek,nt36672e.yaml
>> @@ -24,7 +24,14 @@ properties:
>>     avdd-supply: true
>>     avee-supply: true
>>     port: true
>> -  reset-gpios: true
>> +  reset-gpios:
>> +    maxItems: 1
>> +    description:
>> +      GPIO connected to the reset pin of the panel. The GPIO must be described
>> +      as active high (GPIO_ACTIVE_HIGH), the asserted state releases the panel
> 
> I disagree that it has to be active high, because, since we do not
> represent pin inverters in DT, it depends on board layout. Wording would
> need to be correct if this stays.
> 

I'm all for a better wording.

The described display panel device operates (here resets) according to
the active low signal RESET_N, the device driver is written to interpret
the signal as active high. A signal inverter may be present on a board, but
then the description of this board feature would belong to the board dts,
e.g. in a form of a simple comment around the property.

>> +      from reset. Note that the RESET_N pin is in fact an active low signal,
>> +      the inverted description is kept for compatibility with existing device
>> +      trees, while it deviates from the convention of panel-common.yaml.
> 
> We might fix it at some point, so not sure if it is worth documenting in
> the binding. And what about usage of this binding in other projects
> which implement it correctly?
> 

In the upstream there is only one user qcm6490-idp.dts, and changing
the polarity will be an ABI breaking change, unfortunately.

Here it's a similar story to another one about OV9282 reset-gpios polarity,
it ended up in keeping the polarity of the signal to avoid ABI breakage:

   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/qcom/qrb2210-rb1-vision-mezzanine.dtso#n45

Probably the best way to operate here is to give a clear 'reset-gpios'
property description in the OV9282 sensor or this NT36672E panel dt docs.

-- 
Best wishes,
Vladimir