linux-kernel - Re: [PATCH v2 1/2] dt-bindings: input: touchscreen: goodix: Add no-reset-pull-up property

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Message-ID: <87o6weu6yx.fsf@geanix.com>
Date: Tue, 29 Apr 2025 21:02:14 +0200
From: Esben Haabendal <esben@...nix.com>
To: "Dmitry Torokhov" <dmitry.torokhov@...il.com>
Cc: "Conor Dooley" <conor@...nel.org>,  "Rob Herring" <robh@...nel.org>,
  "Krzysztof Kozlowski" <krzk+dt@...nel.org>,  "Conor Dooley"
 <conor+dt@...nel.org>,  "Hans de Goede" <hdegoede@...hat.com>,
  <linux-input@...r.kernel.org>,  <devicetree@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] dt-bindings: input: touchscreen: goodix: Add
 no-reset-pull-up property

"Dmitry Torokhov" <dmitry.torokhov@...il.com> writes:

> On Tue, Apr 29, 2025 at 05:37:34PM +0200, Esben Haabendal wrote:
>> "Conor Dooley" <conor@...nel.org> writes:
>>
>> > On Tue, Apr 29, 2025 at 11:56:11AM +0200, Esben Haabendal wrote:
>> >> This should be added for boards where there is no pull-up on the reset pin,
>> >> as the driver will otherwise switch the reset signal to high-impedance to
>> >> save power, which obviously not safe without pull-up.
>> >>
>> >> Signed-off-by: Esben Haabendal <esben@...nix.com>
>> >> ---
>> >>  Documentation/devicetree/bindings/input/touchscreen/goodix.yaml | 4 ++++
>> >>  1 file changed, 4 insertions(+)
>> >>
>> >> diff --git a/Documentation/devicetree/bindings/input/touchscreen/goodix.yaml b/Documentation/devicetree/bindings/input/touchscreen/goodix.yaml
>> >> index eb4992f708b70fef93bd4b59b9565123f7c6ad5d..21ac13046b6e021eeb403d854aabc945801dd29f 100644
>> >> --- a/Documentation/devicetree/bindings/input/touchscreen/goodix.yaml
>> >> +++ b/Documentation/devicetree/bindings/input/touchscreen/goodix.yaml
>> >> @@ -45,6 +45,10 @@ properties:
>> >>    reset-gpios:
>> >>      maxItems: 1
>> >>
>> >> +  goodix,no-reset-pull-up:
>> >> +    type: boolean
>> >> +    description: There is no pull-up on reset pin
>> >
>> > I have to wonder, why are these system using the reset property if the
>> > reset is not usable? Shouldn't the property be omitted?
>>
>> The reset are fully functional. It just have to be controlled in
>> push-pull mode.
>>
>> Because of the lack of external pull-up, configuring the reset gpio as
>> input (to save power) puts the reset pin in an unknown state.
>
> How much power do we save by doing this? I don't recall other drivers
> trying to switch reset GPIO into input mode after performing reset...

I don't know.  I also don't recall seeing this in other drivers.  But as
not knowing how much power it is, I did not feel comofortable proposing
to remove it.

/Esben