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: <acde31c5-fe23-4c7b-a823-61ea0958504b@ti.com>
Date: Sat, 1 Mar 2025 03:08:40 +0530
From: "Vankar, Chintan" <c-vankar@...com>
To: Conor Dooley <conor@...nel.org>, Andrew Davis <afd@...com>
CC: 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

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@...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]

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

It is passing dt_binding_check and dtbs_check against correct and
incorrect properties provided in device tree node.

Let me know if you find this correct.

Regards,
Chintan.

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