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

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Date:   Thu, 8 Sep 2022 11:58:50 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Michal Simek <michal.simek@...inx.com>,
        Borislav Petkov <bp@...en8.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Manish Narani <manish.narani@...inx.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Michail Ivanov <Michail.Ivanov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Punnaiah Choudary Kalluri 
        <punnaiah.choudary.kalluri@...inx.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] dt-bindings: memory: snps: Add Baikal-T1 DDRC
 support

On 08/09/2022 11:46, Serge Semin wrote:
> On Mon, Sep 05, 2022 at 12:14:21PM +0200, Krzysztof Kozlowski wrote:
>> 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.
> 
> Ok. But note in such case the compatible string constraints will get
> to be opened for any non-common string. Like this:
> 
> + properties:
> +   compatible:
> +     oneOf:
> +       - const: snps,ddrc-3.80a
> +       - {}

Not really. If you define here specific device compatibles in select,
they must be here as well.

> 
> It's required for the DT-schemas referencing the common one, otherwise
> they will fail DT-nodes evaluation due to the "compatible" property
> missing the vendor-specific string.

o you probably mix here purposes. Either you define common schema or
device specific one. If you define common, usually it does not enforce
any compatibles. You do not need select, no need for compatibles either,
although you can add above syntax if it is valid. If you write here
specific device bindings, then compatibles should be listed. Judging
from what you wrote it's neither this nor that...

Best regards,
Krzysztof