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

[Hugo Villeneuve]

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.

Then would it be ok to remove "col-scan-delay-us" from
gpio-matrix-keypad.yaml and use "line-scan-delay-us" (ABI change) ?

Hugo.

-- 
Hugo Villeneuve <hugo@xxxxxxxxxxx>