linux-kernel - Re: [PATCH 1/6] media: dt-bindings: Document SC8280XP/SM8350 Venus

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Message-ID: <816359f7-ad4d-659f-db39-c971e1b1cd9a@linaro.org>
Date:   Mon, 7 Aug 2023 19:44:27 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
        Vikash Garodia <quic_vgarodia@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] media: dt-bindings: Document SC8280XP/SM8350 Venus

On 07/08/2023 16:02, Konrad Dybcio wrote:
> On 7.08.2023 16:04, Krzysztof Kozlowski wrote:
>> On 07/08/2023 14:41, Konrad Dybcio wrote:
>>> On 5.08.2023 21:29, Krzysztof Kozlowski wrote:
>>>> On 04/08/2023 22:09, Konrad Dybcio wrote:
>>>>> Both of these SoCs implement an IRIS2 block, with SC8280XP being able
>>>>> to clock it a bit higher.
>>>>>
>>>>
>>>> ...
>>>>
>>>>> +
>>>>> +  iommus:
>>>>> +    maxItems: 1
>>>>> +
>>>>> +  video-decoder:
>>>>> +    type: object
>>>>> +
>>>>> +    properties:
>>>>> +      compatible:
>>>>> +        const: venus-decoder
>>>>
>>>> That's not how compatibles are constructed... missing vendor prefix, SoC
>>>> or IP block name.
>>>>
>>>>> +
>>>>> +    required:
>>>>> +      - compatible
>>>>> +
>>>>> +    additionalProperties: false
>>>>
>>>> Why do you need this child node? Child nodes without properties are
>>>> usually useless.
>>> For both comments: I aligned with what was there..
>>>
>>> The driver abuses these compats to probe enc/dec submodules, even though
>>> every Venus implementation (to my knowledge) is implicitly enc/dec capable..
>>
>> Holy crap, I see...
>>
>>>
>>> Perhaps a bigger clean-up is due. I guess I could just create the venc/vdec
>>> devices from the venus core probe and get rid of this fake stuff?
>>
>> Few devices (qcom,msm8996-venus.yaml, sdm660, sdm845) have clocks there,
>> so we actually could stay with these subnodes, just correct the
>> compatibles to a list with correct prefixes:
>>
>> qcom,sc8280xp-venus-decoder + qcom,venus-decoder
> Hm.. looks like pre-845-v2 (with the v2 being "v2 binding" and not
> "v2 chip" or "v2 hardware") these were used to look up clocks but
> then they were moved to the root node.
> 
> I am not quite sure if it makes sense to distinguish e.g.
> sc8280xp-venus-decoder within sc8280xp-venus..
> 
> Perhaps deprecating the "8916 way" (clocks under subnodes), adding
> some boilerplate to look up clocks/pds in both places and converting
> everybody to the "7180 way" way of doing things (clocks under venus),
> and then getting rid of venus encoder/decoder completely (by calling
> device creation from venus probe) would be better. WDYT?
> 
> Konrad

As I understand it though, for some classes of venus hardware - earlier, 
it was possible to have two encoders or two decoders and it really 
didn't - perhaps still doesn't matter which order they are declared in.

That's the logic behind having a compat string that assigns either 
encoder or decoder to one of the logical blocks.

You can have any mixture of
- encoder
- decoder

- encoder
- encoder

- decoder
- decoder

- decoder
- encoder

- encoder

- decoder

I think it should *still* be the case - whether it is a practical 
reality or not, that any of those mapping can be selected and supported.

---
bod