linux-kernel - Re: [PATCH v7 1/7] media: dt-bindings: venus: Add qcm2290 dt schema

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Message-ID: <18d013e5-352e-457b-ba96-3dd19f1cbaed@oss.qualcomm.com>
Date: Fri, 18 Jul 2025 12:02:04 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Jorge Ramirez <jorge.ramirez@....qualcomm.com>
Cc: Bryan O'Donoghue <bryan.odonoghue@...aro.org>, quic_vgarodia@...cinc.com,
        quic_dikshita@...cinc.com, krzk+dt@...nel.org, konradybcio@...nel.org,
        mchehab@...nel.org, andersson@...nel.org, conor+dt@...nel.org,
        amit.kucheria@....qualcomm.com, linux-media@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/7] media: dt-bindings: venus: Add qcm2290 dt schema

On 7/18/25 8:27 AM, Krzysztof Kozlowski wrote:
> On 17/07/2025 19:00, Jorge Ramirez wrote:
>> On 17/07/25 13:16:31, Jorge Ramirez wrote:
>>> On 17/07/25 08:45:17, Krzysztof Kozlowski wrote:
>>>> On 17/07/2025 08:35, Jorge Ramirez wrote:
>>>>> On 17/07/25 00:22:53, Bryan O'Donoghue wrote:
>>>>>> On 15/07/2025 21:47, Jorge Ramirez-Ortiz wrote:
>>>>>>> Add a schema for the venus video encoder/decoder on the qcm2290.
>>>>>>>
>>>>>>> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez@....qualcomm.com>
>>>>>>> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>>>>>> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
>>>>>>> ---
>>>>>>>   .../bindings/media/qcom,qcm2290-venus.yaml    | 127 ++++++++++++++++++
>>>>>>>   1 file changed, 127 insertions(+)
>>>>>>>   create mode 100644 Documentation/devicetree/bindings/media/qcom,qcm2290-venus.yaml
>>>>>>>
>>>>>>> diff --git a/Documentation/devicetree/bindings/media/qcom,qcm2290-venus.yaml b/Documentation/devicetree/bindings/media/qcom,qcm2290-venus.yaml
>>>>>>> new file mode 100644
>>>>>>> index 000000000000..0371f8dd91a3
>>>>>>> --- /dev/null
>>>>>>> +++ b/Documentation/devicetree/bindings/media/qcom,qcm2290-venus.yaml
>>>>>>> @@ -0,0 +1,127 @@
>>>>>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>>>>>> +%YAML 1.2
>>>>>>> +---
>>>>>>> +$id: http://devicetree.org/schemas/media/qcom,qcm2290-venus.yaml#
>>>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>>>>> +
>>>>>>> +title: Qualcomm QCM2290 Venus video encode and decode accelerators
>>>>>>> +
>>>>>>> +maintainers:
>>>>>>> +  - Vikash Garodia <quic_vgarodia@...cinc.com>
>>>>>>
>>>>>> Shouldn't you be on this list ? If you upstream a file I think you should
>>>>>> list yourself as responsible for its glory or its mess.
>>>>>
>>>>> happy to do it. The MAINTAINER's file covered all the files named
>>>>
>>>> This should be the person(s) interested and caring about this hardware,
>>>> which means:
>>>> 1. Subsystem maintainers: no
>>>> 2. Driver maintainers: usually yes
>>>> 3. Author(s) of new hardware support: usually yes
>>>
>>> perfect, will do 
>>>
>>>>
>>>>> schemas/media/*venus* so my understanding was that I shouldn't.
>>>>
>>>> I cannot comment why people decided to go one way or another in other
>>>> code, but it as well could be just incorrect choice thinking only people
>>>> in MAINTAINERS care about hardware.
>>>>
>>>> ...
>>>>
>>>>>>> +
>>>>>>> +        memory-region = <&pil_video_mem>;
>>>>>>> +        iommus = <&apps_smmu 0x860 0x0>,
>>>>>>> +                 <&apps_smmu 0x880 0x0>,
>>>>>>> +                 <&apps_smmu 0x861 0x04>,
>>>>>>> +                 <&apps_smmu 0x863 0x0>,
>>>>>>> +                 <&apps_smmu 0x804 0xe0>;
>>>>>>
>>>>>> You're listing five iommus.
>>>>>>
>>>>>> I understand there's some disagreement about whether or not to list all of
>>>>>> the potential use-cases but, TBH I don't think those are good arguments.
>>>>>>
>>>>>> Unless there's some technical prohibition I can't think of listing all five
>>>>>> maxItems:5 .. let's just do that.
>>>>>
>>>>> since the device tree should describe hardware and not policy, and the
>>>>> driver seems to be able to ignore the unused SIDs I think this is the
>>>>> right thing to do.
>>>>
>>>>
>>>> It was never about the driver but about whether you should describe in
>>>> DTS for non-secure world the entries which are secure world. The answer
>>>> in general is that you can and there will be benefits (e.g. sharing DTS
>>>> with secure world implementations).
>>>
>>> all right, sounds good then, thanks
>>
>> Not sure if I’ve shared this before, but following an internal
>> discussion, I think it’s worth highlighting a functional dependency in
>> the current kernel:
>>
>>  - the driver only works if the first two IOMMUs in the list — the
>> non-secure ones — are placed at the beginning. Reordering them breaks
>> functionality, which introduces unexpected fragility.
>>
>> Regardless, this seems like a valid concern to me — a driver shouldn't
>> rely on the order of phandles — and I just wanted to make sure you're
>> aware of it before I post a v8 (likely sometime next week or the
>> following, as I’ll be taking a short break soon).
> 
> 
> Hm? Order of lists is strictly defined. That's actually an overlook that
> we never do it for iommus, but the core rule stays.

(FWIW "items:" is an ordered list, "enum:" is unordered)

Konrad