Re: [PATCH 1/3] dt-bindings: i3c: renesas,i3c: Document analog noise filter control

[Frank Li]

On Mon, Oct 26, 2026 at 04:21:06PM +0000, Diogo Ivo wrote:
> Hi Frank,
>
> On 10/20/2026 8:18 PM, Frank Li wrote:
> > On Tue, Oct 20, 2026 at 10:36:26AM +0100, Diogo Ivo wrote:
> > > The analog noise filter for the input terminals (I3C_SDA, I3C_SCL) of
> > > the Renesas I3C controller is controlled through the SYS_I3C_CFG
> > > register of the system controller. Document the
> > > renesas,analog-noise-filter property, which references the system
> > > controller together with the offset of the SYS_I3C_CFG register and
> > > the state of the filter: 1 enables the filter and 0 bypasses it.
> > >
> > > The property is optional: device trees not providing it keep the
> > > filter at its reset value.
> > >
> > > Signed-off-by: Diogo Ivo <diogo.ivo.sx@xxxxxxxxxxx>
> > > ---
> > >   .../devicetree/bindings/i3c/renesas,i3c.yaml          | 19 +++++++++++++++++++
> > >   1 file changed, 19 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/i3c/renesas,i3c.yaml b/Documentation/devicetree/bindings/i3c/renesas,i3c.yaml
> > > index 08fcea89a015..381807844351 100644
> > > --- a/Documentation/devicetree/bindings/i3c/renesas,i3c.yaml
> > > +++ b/Documentation/devicetree/bindings/i3c/renesas,i3c.yaml
> > > @@ -96,6 +96,25 @@ properties:
> > >         - const: presetn
> > >         - const: tresetn
> > >
> > > +  renesas,analog-noise-filter:
> > > +    $ref: /schemas/types.yaml#/definitions/phandle-array
> >
> > I don't like this syscon property, look like it is one kind pad propterty.
> > Is it possible model as pinctrl?
>
> On the RZ/G3L and RZ/G3S this filter is not controlled on the pin
> controller's address space but in the SYSC address space (hence the
> need for the sysc phandle).
>
> There are a few factors weighing against modeling this as pinctrl.
>
> The first is that the physical pads used by I3C are multiplexed between it
> and for example RIIC3, so we are not filtering the pad but the internal path
> of the I3C IP. The pinctrl does indeed have some controls for the pad's
> digital filters, that apply to whatever block is multiplexed to the pad.
>
> Besides this, even if it were moved to pinctrl we would still need the sysc
> reference, as the pfc driver would need a way to reference the sysc address
> space.

System allows multi pinctrl devices. your syscon can work as pinctrl provider

pinctrl-0 = <&your nomral pinctrl>, <&syscon i3c ... > ;

The key problem is if model is resonable. Syscon is simple, but have not
good abstract.

Frank

>
> With this, I think that having a DT property is the best approach. However,
> the form of the property can be changed if you are against this particular
> one. For example, the register offset can be moved to platform_data in the
> I3C driver:
>
>  - renesas,analog-noise-filter = <&sysc 0/1> at the SoC level
>
> or I can also split it into two properties.
>
> What approach would work better here? Me I'm leaning towards having
> renesas,analog-digital-filter.
>
> Best regards,
> Diogo
>
> >
> > Frank
> >
> > > +    description:
> > > +      Analog noise filter for the I3C input signals (I3C_SDA, I3C_SCL),
> > > +      controlled through the SYS_I3C_CFG register of the system
> > > +      controller (SYSC). Three entries specifying the system controller,
> > > +      the offset of the SYS_I3C_CFG register and the state of the filter.
> > > +      If not present, the filter keeps its reset state.
> > > +    items:
> > > +      - items:
> > > +          - description: phandle to the system controller node
> > > +          - description: offset of the SYS_I3C_CFG register within the SYSC
> > > +          - enum: [0, 1]
> > > +            description: |
> > > +              state of the analog noise filter:
> > > +               - 1: enable the filter, performing noise reduction on the
> > > +                 I3C_SDA and I3C_SCL input signals
> > > +               - 0: bypass the filter
> > > +
> > >   required:
> > >     - compatible
> > >     - reg
> > >
> > > --
> > > 2.56.0
> > >
>