linux-kernel - Re: [PATCH v4 4/6] dt-bindings: touchscreen: fsl,imx6ul-tsc: support glitch thresold

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Message-ID: <20250917-unhidden-foothill-7c103245be1f@spud>
Date: Wed, 17 Sep 2025 20:26:49 +0100
From: Conor Dooley <conor@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Dario Binacchi <dario.binacchi@...rulasolutions.com>,
	linux-kernel@...r.kernel.org, linux-amarula@...rulasolutions.com,
	Conor Dooley <conor+dt@...nel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Fabio Estevam <festevam@...il.com>, Haibo Chen <haibo.chen@....com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Rob Herring <robh@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>, devicetree@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-input@...r.kernel.org
Subject: Re: [PATCH v4 4/6] dt-bindings: touchscreen: fsl,imx6ul-tsc: support
 glitch thresold

On Wed, Sep 17, 2025 at 12:07:44PM -0400, Frank Li wrote:
> On Wed, Sep 17, 2025 at 10:05:09AM +0200, Dario Binacchi wrote:
> > Support the touchscreen-glitch-threshold-ns property.
> >
> > Drivers must convert this value to IPG clock cycles and map it to one of
> 
> binding descript hardware, not drivers. So below sentence should be better.
> 
> "TSC only supports the four discrete thresholds, counted by IPG clock cycles.
> See SC_DEBUG_MODE2 register."
> 
> > the four discrete thresholds exposed by the TSC_DEBUG_MODE2 register:
> >
> >   0: 8191 IPG cycles
> >   1: 4095 IPG cycles
> >   2: 2047 IPG cycles
> >   3: 1023 IPG cycles
> >
> > Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> >
> > ---
> >
> > Changes in v4:
> > - Adjust property description following the suggestions of
> >   Conor Dooley and Frank Li.
> > - Update the commit description.
> >
> > Changes in v3:
> > - Remove the final part of the description that refers to
> >   implementation details.
> >
> >  .../bindings/input/touchscreen/fsl,imx6ul-tsc.yaml | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/input/touchscreen/fsl,imx6ul-tsc.yaml b/Documentation/devicetree/bindings/input/touchscreen/fsl,imx6ul-tsc.yaml
> > index 678756ad0f92..1975f741cf3d 100644
> > --- a/Documentation/devicetree/bindings/input/touchscreen/fsl,imx6ul-tsc.yaml
> > +++ b/Documentation/devicetree/bindings/input/touchscreen/fsl,imx6ul-tsc.yaml
> > @@ -62,6 +62,20 @@ properties:
> >      description: Number of data samples which are averaged for each read.
> >      enum: [ 1, 4, 8, 16, 32 ]
> >
> > +  touchscreen-glitch-threshold-ns:
> > +    description: |
> > +      Minimum duration in nanoseconds a signal must remain stable
> > +      to be considered valid.
> > +
> > +      Drivers must convert this value to IPG clock cycles and map
> > +      it to one of the four discrete thresholds exposed by the
> > +      TSC_DEBUG_MODE2 register:
> 
> same as commit messsage, talk about hardware.

This is fine. It's a generic comment about what must be done with the
property by software that helps people understand how to populate it.
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>


> > +        0: 8191 IPG cycles
> > +        1: 4095 IPG cycles
> > +        2: 2047 IPG cycles
> > +        3: 1023 IPG cycles
> > +
> 
> This case genenerally need enum 4 values, but it relates IPG frequency.
> I have not idea how to restrict it base on clk frequency. May DT mainatainer
> have idea.

I don't see how you really can restrict it based on the frequency of a
clock that can probably be varied at runtime.

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