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

[Conor Dooley <conor@kernel.org>]

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On Sat, Mar 01, 2025 at 03:08:40AM +0530, Vankar, Chintan wrote:
> Hello Conor, Andrew,
> 
> On 3/1/2025 12:22 AM, Conor Dooley wrote:
> > 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@ti.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
> 
> Thanks for reviewing this patch.
> 
> For the use-case we have following three rules to be followed:
> 1. "mux-reg-masks" and "mux-reg-masks-state" should be mutually
>    exclusive.
> 2. "mux-reg-masks-state" and "idle-states" should also be mutually
>    exclusive.
> 3. If "mux-reg-masks" is present then "idle-states" might or might not
>    be there.
> 
> For the above conditions I have tried to write a binding as:
> 
> allOf:
>   - not:
>       required: [mux-reg-masks, mux-reg-masks-state]
> 
>   - if:
>       required: [mux-reg-masks-state]
>     then:
>       not:
>         required: [idle-states]

Why'd you pick two different syntax here?
The normal syntax for mutual exclusion is:
if:
  required:
    - foo
then:
  properties:
    foobar: false


> 

>   - if:
>       required: [mux-reg-masks]
>     then:
>       properties:
>         idle-states:
>           description: It can be present with mux-reg-masks, but not
> required

This one here is the default, I don't think it needs an if/else.


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