Subject: Re: [PATCH v13 1/4] dt-bindings: dmaengine: Add doc for tegra gpcdma
From:   Jon Hunter <jonathanh@nvidia.com>
To:     Akhil R <akhilrajeev@nvidia.com>, Rob Herring <robh@kernel.org>
Cc:     "dan.j.williams@intel.com" <dan.j.williams@intel.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
        Krishna Yarlagadda <kyarlagadda@nvidia.com>,
        Laxman Dewangan <ldewangan@nvidia.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        "p.zabel@pengutronix.de" <p.zabel@pengutronix.de>,
        Rajesh Gumasta <rgumasta@nvidia.com>,
        "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        "vkoul@kernel.org" <vkoul@kernel.org>
References: <1637573292-13214-1-git-send-email-akhilrajeev@nvidia.com>
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Date:   Wed, 1 Dec 2021 14:33:31 +0000
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On 30/11/2021 09:34, Jon Hunter wrote:

...

>>>> +title: NVIDIA Tegra GPC DMA Controller Device Tree Bindings
>>>> +
>>>> +description: |
>>>> +  The Tegra General Purpose Central (GPC) DMA controller is used for
>>>> +faster
>>>> +  data transfers between memory to memory, memory to device and
>>>> +device to
>>>> +  memory.
>>>> +
>>>> +maintainers:
>>>> +  - Jon Hunter <jonathanh@nvidia.com>
>>>> +  - Rajesh Gumasta <rgumasta@nvidia.com>
>>>> +
>>>> +allOf:
>>>> +  - $ref: "dma-controller.yaml#"
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    oneOf:
>>>> +      - const: nvidia,tegra186-gpcdma
>>>> +      - items:
>>>> +         - const: nvidia,tegra186-gpcdma
>>>> +         - const: nvidia,tegra194-gpcdma
>>>
>>> Still not how 'compatible' works nor what I wrote out for you.
>> I thought '186' and '194' got interchanged in your previous comment 
>> because it is 194
>> which is the superset of 186 and have got more features than 186.
>> Or probably I did not understand the idea correctly yet. 
> 
> Hi Rob, this is the way around that we want it. Tegra194 is backward 
> compatible with Tegra186. The above does align with what you mentioned 
> before, so I am also not clear what the issue is with the above?


Now I think I understand. It is the order of the 'items' here that is 
key. So what we want is ...

   compatible:
     oneOf:
       - const: nvidia,tegra186-gpcdma
       - items:
          - const: nvidia,tegra194-gpcdma
          - const: nvidia,tegra186-gpcdma

At least this makes the dt_binding_check happy :-)

Jon

-- 
nvpublic