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

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Message-ID: <5afbaf46-bbb1-47d8-84aa-29b18987564f@kernel.org>
Date: Fri, 18 Jul 2025 08:27:23 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: 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 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.


Best regards,
Krzysztof