Re: [PATCH v2 4/6] dt-bindings: gpu: v3d: Add SMS to the registers' list

[Krzysztof Kozlowski <krzk@kernel.org>]

On 10/03/2025 14:15, Maíra Canal wrote:
> Hi Krzysztof,
> 
> On 3/10/25 09:55, Krzysztof Kozlowski wrote:
>> On 10/03/2025 12:57, Maíra Canal wrote:
>>>>
>>>>> Signed-off-by: Maíra Canal <mcanal@igalia.com>
>>>>> ---
>>>>>    .../devicetree/bindings/gpu/brcm,bcm-v3d.yaml      | 60 ++++++++++++++++++++--
>>>>>    1 file changed, 55 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.yaml b/Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.yaml
>>>>> index dc078ceeca9ac3447ba54a7c8830821f0b2a7f9f..c0caee055e8c18dbcac0e51aa192951996545695 100644
>>>>> --- a/Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.yaml
>>>>> +++ b/Documentation/devicetree/bindings/gpu/brcm,bcm-v3d.yaml
>>>>> @@ -27,15 +27,12 @@ properties:
>>>>>          - description: core0 register (required)
>>>>>          - description: GCA cache controller register (if GCA controller present)
>>>>>          - description: bridge register (if no external reset controller)
>>>>> +      - description: SMS register (if SMS controller present)
>>>>
>>>> This lists five items, but you say you have max 4?
>>>
>>> V3D 3.1 uses hub, core0, gca, and bridge (optional)
>>> V3D 4.1 and 4.2 uses hub, core, and bridge (optional)
>>> V3D 7.1 uses hub, core0, sms, and bridge (optional)
>>>
>>> Therefore, for a given DT, you will have 4 items max.
>>
>> And how many items do you have here?
>>
>>>
>>>>
>>>>>        minItems: 2
>>>>>    
>>>>>      reg-names:
>>>>> -    items:
>>>>> -      - const: hub
>>>>> -      - const: core0
>>>>> -      - enum: [ bridge, gca ]
>>>>> -      - enum: [ bridge, gca ]
>>>>>        minItems: 2
>>>>> +    maxItems: 4
>>>>
>>>> So here 4, but earlier 5? These must come in sync.
>>>
>>> I added maxItems for reg in the allOf section.
>>
>> I don't think you answer the comments. I said you listed earlier 5 items
>> and then you answered with saying devices have 4 items. Here I said
>> these properties must be synced and you said why you added maxItems...
>> Not related, read again the feedback.
> 
> I'm sorry, I don't usually write DTBs. I believe what I need is to
> specify the reg items for each compatible, right?

You need to list four items in 'reg' and last items' description would
need to describe two different sets.

And commit msg must explain why now this device needs to use sms, not
gca. Why you cannot use the gca range instead of sms? So many questions.

> 
>>
>>
>>>
>>>>
>>>>>    
>>>>>      interrupts:
>>>>>        items:
>>>>> @@ -60,6 +57,59 @@ required:
>>>>>    
>>>>>    additionalProperties: false
>>>>>    
>>>>> +allOf:
>>>>
>>>> This goes above additionalProperties.
>>>
>>> Got it.
>>>
>>>>
>>>>> +  - if:
>>>>> +      properties:
>>>>> +        compatible:
>>>>> +          contains:
>>>>> +            enum:
>>>>> +              - brcm,2711-v3d
>>>>> +              - brcm,7278-v3d
>>>>> +    then:
>>>>> +      properties:
>>>>> +        reg:
>>>>> +          minItems: 2
>>>>> +          maxItems: 3
>>>>> +        reg-names:
>>>>> +          items:
>>>>> +            - const: hub
>>>>> +            - const: core0
>>>>> +            - const: bridge
>>>>
>>>> Again un-synced lists.
>>>
>>> Sorry, what do you mean by un-synced lists?
>>
>> xxx and xxx-names must have the same constraints. They do not have here.
>> You have two different constraints and you can test your DTS to see that.
>  >
> 
> I used `make dt_binding_check` to test it and it didn't catch any
> errors.

So change the example to have one list with two items and second list
with three items. Is it correct DTS? No. Does this pass tests? Yes.

> 
>>>
>>>>
>>>>> +  - if:
>>>>> +      properties:
>>>>> +        compatible:
>>>>> +          contains:
>>>>> +            const: brcm,2712-v3d
>>>>> +    then:
>>>>> +      properties:
>>>>> +        reg:
>>>>> +          minItems: 3
>>>>> +          maxItems: 4
>>>>> +        reg-names:
>>>>> +          items:
>>>>> +            - const: hub
>>>>> +            - const: core0
>>>>> +            - enum: [ bridge, sms ]
>>>>> +            - enum: [ bridge, sms ]
>>>>> +          minItems: 3
>>>>
>>>> Why is this flexible?
>>>
>>> I cannot guarantee the order and bridge is optional.
>>
>> Hm? You must guarantee the order and I do not understand why this needs
>> some sort of exception from all other bindings that only here you cannot
>> guarantee the order.
> 
> I'm trying to keep backwards compatibility. This binding exists for many
> years and it always used "enum: [ bridge, gca ]".

But it is now sms, not gca,, so I do not see how the ABI is preserved.

Best regards,
Krzysztof