Re: [PATCH 02/13] dt-bindings: memory: snps: Add Baikal-T1 DDRC support

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 26/08/2022 11:54, Serge Semin wrote:
> On Tue, Aug 23, 2022 at 11:12:28AM +0300, Krzysztof Kozlowski wrote:
>> On 22/08/2022 22:19, Serge Semin wrote:
>>> Baikal-T1 DDR controller is based on the DW uMCTL2 DDRC IP-core v2.51a
>>> with up to DDR3 protocol capability and 32-bit data bus + 8-bit ECC. There
>>> are individual IRQs for each ECC and DFI events.The dedicated scrubber
>>
> 
>> Missing space before "The".
> 
> Ok. Thanks.
> 
>>
>>> clock source is absent since it's fully synchronous to the core clock.
>>
> 
>> You need allOf:if-then restricting this per variant.
> 
> I really don't like the allOf-if-if-etc pattern because it gets to be
> very bulky if all the vendor-specific and generic platform
> peculiarities are placed in there. I am more keen of having a
> generic DT-schema which would be then allOf-ed by the vendor-specific
> device bindings. What do you think I'd provide such design in this
> case too?

Sure, it would work.

> 
> But I'll need to move the compatible property definition to the
> "select" property. Like this:
> 
> Documentation/devicetree/bindings/memory-controllers/snps,dw-umctl2-ddrc.yaml:
> +[...]
> +# Please create a separate DT-schema for your DW uMCTL2 DDR controller
> +# and make sure it's assigned with the vendor-specific compatible string.
> +select:
> +  properties:
> +    compatible:
> +      oneOf:
> +        - deprecated: true
> +          description: Synopsys DW uMCTL2 DDR controller v3.80a
> +          const: snps,ddrc-3.80a
> +        - description: Synopsys DW uMCTL2 DDR controller
> +          const: snps,dw-umctl2-ddrc
> +        - description: Xilinx ZynqMP DDR controller v2.40a
> +          const: xlnx,zynqmp-ddrc-2.40a
> +  required:
> +    - compatible

Not entirely. If you need select, then add it with compatibles, but all
descriptions and deprecated are staying in properties.


> +
> +properties:
> +  compatible: true
> +[...]
> +required:
> +  - compatible
> +  - reg
> +  - interrupts
> +
> +additionalProperties: true
> 
> After that the "snps,dw-umctl2-ddrc.yaml" schema can be referenced in the
> allOf composition. Like this:
> 
> Documentation/devicetree/bindings/memory-controllers/baikal,bt1-ddrc.yaml:
> +[...]
> +allOf:
> +  - $ref: /schemas/memory-controllers/snps,dw-umctl2-ddrc.yaml#
> +[...]
> 
> At the same time the generic DT-schema will be used to evaluate the
> "snps,ddrc-3.80a", "snps,dw-umctl2-ddrc" and "xlnx,zynqmp-ddrc-2.40a"
> device nodes as before. What do you think about that?
> 
> One big positive side of this that even though the generic schema
> can't define the IRQ/resets/clocks phandlers order because various
> platforms may have different external signals setup, the
> vendor-specific schema can and should. So I'll be able to describe the
> Baikal-T1 DDRC specific properties (clocks, clock-names, interrupts,
> interrupt-names, etc) in much more details including the reference
> signals order what you asked in the previous patch review.

It's ok. You need then second schema for your device, because something
must end with additional/unevaluatedProperties false.

Best regards,
Krzysztof