Re: [PATCH v2 1/2] dt-bindings: input: add GPIO charlieplex keypad

[Rob Herring]

On Tue, Feb 24, 2026 at 2:40 PM Hugo Villeneuve <hugo@xxxxxxxxxxx> wrote:
>
> Hi Rob,
>
> On Mon, 23 Feb 2026 17:23:33 -0600
> Rob Herring <robh@xxxxxxxxxx> wrote:
>
> > On Mon, Feb 23, 2026 at 12:47 PM Hugo Villeneuve <hugo@xxxxxxxxxxx> wrote:
> > >
> > > Hi Rob,
> > >
> > > On Mon, 23 Feb 2026 11:57:06 -0600
> > > Rob Herring <robh@xxxxxxxxxx> wrote:
> > >
> > > > On Fri, Feb 13, 2026 at 12:14:25PM -0500, Hugo Villeneuve wrote:
> > > > > From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
> > > > >
> > > > > Add DT bindings for GPIO charlieplex keypad.
> > > > >
> > > > > Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
> > > > > ---
> > > > >  .../input/gpio-charlieplex-keypad.yaml        | 82 +++++++++++++++++++
> > > > >  1 file changed, 82 insertions(+)
> > > > >  create mode 100644 Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml b/Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
> > > > > new file mode 100644
> > > > > index 0000000000000..1672491a75a85
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/input/gpio-charlieplex-keypad.yaml
> > > > > @@ -0,0 +1,82 @@
> > > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > > +%YAML 1.2
> > > > > +---
> > > > > +
> > > > > +$id: http://devicetree.org/schemas/input/gpio-charlieplex-keypad.yaml#
> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > +
> > > > > +title: GPIO charlieplex keypad
> > > > > +
> > > > > +maintainers:
> > > > > +  - Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
> > > > > +
> > > > > +description:
> > > > > +  The charlieplex keypad supports N^2)-N different key combinations (where N is
> > > > > +  the number of lines). Key presses and releases are detected by configuring
> > > > > +  only one line as output at a time, and reading other line states. This process
> > > > > +  is repeated for each line.
> > > > > +  This mechanism doesn't allow to detect simultaneous key presses.
> > > > > +
> > > > > +allOf:
> > > > > +  - $ref: input.yaml#
> > > > > +  - $ref: /schemas/input/matrix-keymap.yaml#
> > > > > +
> > > > > +properties:
> > > > > +  compatible:
> > > > > +    const: gpio-charlieplex-keypad
> > > > > +
> > > > > +  autorepeat: true
> > > > > +
> > > > > +  line-scan-delay-us:
> > > > > +    description:
> > > > > +      Delay, measured in microseconds, that is needed
> > > > > +      before we can scan keypad after activating one line.
> > > > > +    default: 0
> > > >
> > > > Isn't this the same as "col-scan-delay-us" in gpio-matrix-keypad.yaml?
> > > > If so, move it to matrix-keymap.yaml to re-use it here.
> > >
> > > It is used in a similar fashion, but for charlieplex keyboard, there is
> > > no concept of "rows" and "columns". There are only
> > > lines, which are all equivalent in functionality.
> > >
> > > > If not, there's a bunch of other scan delay properties just from
> > > > grepping "delay" in the input bindings. Surely we can define something
> > > > common.
> > >
> > > Most of those delays refer to something quite different than what
> > > "col-scan-delay-us" or "line-scan-delay-us" are used for (it is a delay
> > > that we wait when activating a GPIO before we can safely/reliably read
> > > other GPIOs connected thru its circuitry).
> > >
> > > Maybe "col-scan-delay-us" and "line-scan-delay-us" could be
> > > combined into a common "line-scan-delay-us" ("line" is more generic
> > > than column), and defined in matrix-keymap.yaml.
> >
> > What about "scan-delay-us"? I would assume all the scan delay
> > properties are just the delay after changing the outputs to reading
> > the inputs.
>
> They are for gpio-matrix-keypad.yaml and this binding, but not for
> others. Most scan delay properties refer to the period or
> interval between successive scans.
>
> So for my binding, "settling-time-us" would be more accurate and a
> better property name (it is also used in adc.yaml).

Let's go with that.

>
> Looking into a common place to define this new property, I stumbled
> upon gpio-delay.yaml, so maybe I do not need this new property at all
> and simply define a gpio-delay node if needed (and add it to this
> binding example)?
>
> I tested this and it works, although it requires a patch to the
> gpio-aggregator driver, because for now it respect the delay only
> when changing the output value, not when switching between input and
> output like I do in my driver.
>
> With my patch, it works ok.

I would not use gpio-delay here.

Rob