linux-kernel - Re: [PATCH v5 3/6] dt-bindings: touchscreen: add touchscreen-glitch-threshold-ns property

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Message-ID: <20250919143831.GA862818-robh@kernel.org>
Date: Fri, 19 Sep 2025 09:38:31 -0500
From: Rob Herring <robh@...nel.org>
To: Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc: linux-kernel@...r.kernel.org, Frank Li <Frank.Li@....com>,
	linux-amarula@...rulasolutions.com,
	Conor Dooley <conor.dooley@...rochip.com>,
	Conor Dooley <conor+dt@...nel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Javier Carrasco <javier.carrasco@...fvision.net>,
	Jeff LaBundy <jeff@...undy.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	devicetree@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH v5 3/6] dt-bindings: touchscreen: add
 touchscreen-glitch-threshold-ns property

On Thu, Sep 18, 2025 at 10:37:37PM +0200, Dario Binacchi wrote:
> On Thu, Sep 18, 2025 at 10:04 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Thu, Sep 18, 2025 at 05:52:31PM +0200, Dario Binacchi wrote:
> > > Add support for glitch threshold configuration. A detected signal is valid
> > > only if it lasts longer than the set threshold; otherwise, it is regarded
> > > as a glitch.
> > >
> > > Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> > > Acked-by: Conor Dooley <conor.dooley@...rochip.com>
> > >
> > > ---
> > >
> > > Changes in v5:
> > > - Add Acked-by tag of Conor Dooley
> > >
> > > Changes in v2:
> > > - Added in v2.
> > >
> > >  .../devicetree/bindings/input/touchscreen/touchscreen.yaml    | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml b/Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml
> > > index 3e3572aa483a..a60b4d08620d 100644
> > > --- a/Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml
> > > +++ b/Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml
> > > @@ -206,6 +206,10 @@ properties:
> > >
> > >          unevaluatedProperties: false
> > >
> > > +  touchscreen-glitch-threshold-ns:
> > > +    description: Minimum duration in nanoseconds a signal must remain stable
> > > +      to be considered valid.
> >
> > What's wrong with debounce-delay-ms?
> 
> Do you mean that I should rename touchscreen-glitch-threshold-ns to
> debounce-delay-ms?

I mean that's the common property we already have, so use it or explain 
why you aren't using it. I suppose the definition is technically a bit 
different if it's purely a s/w delay vs. h/w monitoring of the signal 
state. I don't think it matters if the interpretation by each driver is 
a bit different.

Maybe msec is not enough resolution for you could be another reason? 
Looks like your h/w supports that assuming the clock frequency is 10s 
of MHz. But are touchscreen glitches really in sub msec times? Not in my 
experience, but that's 20 years ago on resistive touchscreens...

Rob