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

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Message-ID: <87wmb3t5uj.fsf@geanix.com>
Date: Tue, 29 Apr 2025 16:11:48 +0200
From: Esben Haabendal <esben@...nix.com>
To: "Dmitry Torokhov" <dmitry.torokhov@...il.com>
Cc: "Krzysztof Kozlowski" <krzk@...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 1/2] dt-bindings: input: touchscreen: goodix: Add
 no-reset-pull-up property

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

> On Mon, Apr 28, 2025 at 07:58:55AM +0000, Esben Haabendal wrote:
>> On Monday, April 28th, 2025 at 09:48, Krzysztof Kozlowski <krzk@...nel.org> wrote:
>> > On Tue, Apr 22, 2025 at 05:15:02PM GMT, 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..7e5c4b98f2cb1ef61798252ea5c573068a46d4aa 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
>> > >
>> > > + no-reset-pull-up:
>> >
>> > Is this common property? Where is it defined? Otherwise missing vendor
>> > prefix.
>>
>> Good question. When is something a common property?
>>
>> The idea of marking something as not having a pull-up on the reset pin could be considered a common thing I guess.
>> But for now, I am defining it for the goodix driver only, as I am only aware of these devices needing to handle it in a special way.
>>
>> Should I rename it to goodix,no-reset-pull-up?
>
> We already have GPIO_PULL_UP/GPIO_PULL_DOWN flags available in GPIO
> bindings. So maybe the correct way is to have the driver rely on them
> and only leave the reset line in high-impedance mode if GPIO tells it
> that there is a pull-up?

As I understand GPIO_PULL_UP/GPIO_PULL_DOWN flags in bindings, they
indicate that pull-up/pull-down is to be configured for the gpio.

This is different to what I am expressing with goodix,no-reset-pull-up,
as I am expressing the lack of external pull-up on the signal. Without
that, the goodix driver assumes that an external pull-up is mounted, and
that the gpio pin can be set to high impedance, and the external pull-up
will ensure that it stays high.

How do you propose that we can use GPIO_PULL_UP/GPIO_PULL_DOWN flags for
this purpose?

/Esben