linux-kernel - Re: [RFC PATCH 1/2] devicetree: bindings: mux: reg-mux: Update bindings for reg-mux for new property

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Message-ID: <20250228-recipient-unlinked-271fe63d7335@spud>
Date: Fri, 28 Feb 2025 18:52:48 +0000
From: Conor Dooley <conor@...nel.org>
To: Andrew Davis <afd@...com>
Cc: Chintan Vankar <c-vankar@...com>, Conor Dooley <conor+dt@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Rob Herring <robh@...nel.org>, Peter Rosin <peda@...ntia.se>,
	tglx@...utronix.de, gregkh@...uxfoundation.org, vigneshr@...com,
	nm@...com, s-vadapalli@...com, danishanwar@...com,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] devicetree: bindings: mux: reg-mux: Update
 bindings for reg-mux for new property

On Thu, Feb 27, 2025 at 03:26:31PM -0600, Andrew Davis wrote:
> On 2/27/25 2:22 PM, Chintan Vankar wrote:
> > DT-binding of reg-mux is defined in such a way that one need to provide
> > register offset and mask in a "mux-reg-masks" property and corresponding
> > register value in "idle-states" property. This constraint forces to define
> > these values in such a way that "mux-reg-masks" and "idle-states" must be
> > in sync with each other. This implementation would be more complex if
> > specific register or set of registers need to be configured which has
> > large memory space. Introduce a new property "mux-reg-masks-state" which
> > allow to specify offset, mask and value as a tuple in a single property.
> > 
> > Signed-off-by: Chintan Vankar <c-vankar@...com>
> > ---
> >   .../devicetree/bindings/mux/reg-mux.yaml      | 29 +++++++++++++++++--
> >   1 file changed, 27 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/mux/reg-mux.yaml b/Documentation/devicetree/bindings/mux/reg-mux.yaml
> > index dc4be092fc2f..a73c5efcf860 100644
> > --- a/Documentation/devicetree/bindings/mux/reg-mux.yaml
> > +++ b/Documentation/devicetree/bindings/mux/reg-mux.yaml
> > @@ -32,11 +32,36 @@ properties:
> >           - description: pre-shifted bitfield mask
> >       description: Each entry pair describes a single mux control.
> > -  idle-states: true
> > +  idle-states:
> > +    description: Each entry describes mux register state.
> > +
> > +  mux-reg-masks-state:
> > +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> > +    items:
> > +      items:
> > +        - description: register offset
> > +        - description: pre-shifted bitfield mask
> > +        - description: register value to be set
> > +    description: This property is an extension of mux-reg-masks which
> > +                 allows specifying register offset, mask and register
> > +                 value to be set in a single property.
> > +
> > +allOf:
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            enum:
> > +              - reg-mux
> > +              - mmio-mux
> 
> These are the only two possible compatibles, is this "if" check needed?

Aye.

> > +    then:
> > +      properties:
> > +        mux-reg-masks: true
> > +        mux-reg-masks-state: true
> 
> You need one, but cannot have both, right? There should be some
> way to describe that.
> 
> Also an example added below would be good.

From the example schema:
# if/then schema can be used to handle conditions on a property affecting
# another property. A typical case is a specific 'compatible' value changes the
# constraints on other properties.
#
# For multiple 'if' schema, group them under an 'allOf'.
#
# If the conditionals become too unweldy, then it may be better to just split
# the binding into separate schema documents.
allOf:
  - if:
      properties:
        compatible:
          contains:
            const: vendor,soc2-ip
    then:
      required:
        - foo-supply
    else:
      # If otherwise the property is not allowed:
      properties:
        foo-supply: false

What's missing from here is making one of the properties required,
so
oneOf:
  - required:
      - masks
  - required:
      - masks-state

> 
> Andrew
> 
> > +      maxItems: 1
> >   required:
> >     - compatible
> > -  - mux-reg-masks
> >     - '#mux-control-cells'
> >   additionalProperties: false

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