linux-kernel - Re: [PATCH] media: dt-bindings: qcom,sm8550-iris: Do not reference legacy venus properties

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Message-ID: <05d40a3b-cc13-b704-cac7-0ecbeea0e59d@quicinc.com>
Date: Thu, 28 Aug 2025 19:19:18 +0530
From: Vikash Garodia <quic_vgarodia@...cinc.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Mukesh Ojha
	<mukesh.ojha@....qualcomm.com>
CC: Dikshita Agarwal <quic_dikshita@...cinc.com>,
        Abhinav Kumar
	<abhinav.kumar@...ux.dev>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: dt-bindings: qcom,sm8550-iris: Do not reference
 legacy venus properties


On 8/25/2025 5:32 PM, Krzysztof Kozlowski wrote:
> On 25/08/2025 13:37, Mukesh Ojha wrote:
>> On Sat, Aug 23, 2025 at 05:53:50PM +0200, Krzysztof Kozlowski wrote:
>>> The Qualcomm SoC Iris video codec is an evolution of previous Venus and
>>> it comes with its own Iris Linux drivers.  These new drivers were
>>> accepted under condition they actually improve state of afairs, instead
>>> of duplicating old, legacy solutions.
>>>
>>> Unfortunately binding still references common parts of Venus without
>>> actual need and benefit.  For example Iris does not use fake
>>> "video-firmware" device node (fake because there is no actual device
>>> underlying it and it was added only to work around some Linux issues
>>> with IOMMU mappings).
>>>
>>> Stop referencing venus-common schema in the new Qualcomm Iris bindings
>>> and move all necessary properties, except unused "video-firmware" (no
>>> driver usage, no DTS).
>>>
>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>> ---
>>>  .../devicetree/bindings/media/qcom,sm8550-iris.yaml | 13 ++++++++++++-
>>>  1 file changed, 12 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml b/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
>>> index c79bf2101812..320227f437a1 100644
>>> --- a/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
>>> +++ b/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
>>> @@ -26,6 +26,9 @@ properties:
>>>            - qcom,sm8550-iris
>>>            - qcom,sm8650-iris
>>>  
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>>    power-domains:
>>>      maxItems: 4
>>>  
>>> @@ -45,6 +48,12 @@ properties:
>>>        - const: core
>>>        - const: vcodec0_core
>>>  
>>> +  firmware-name:
>>> +    maxItems: 1
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>>    interconnects:
>>>      maxItems: 2
>>>  
>>> @@ -69,6 +78,9 @@ properties:
>>>  
>>>    dma-coherent: true
>>>  
>>> +  memory-region:
>>> +    maxItems: 1
>>> +
>>>    operating-points-v2: true
>>>  
>>>    opp-table:
>>> @@ -85,7 +97,6 @@ required:
>>>    - dma-coherent
>>>  
>>>  allOf:
>>> -  - $ref: qcom,venus-common.yaml#
>>>    - if:
>>
>> Saw your reply on 
>> https://lore.kernel.org/lkml/59951c47-1015-4598-a885-25f8f1a27c64@kernel.org/
>>
>> Just trying to understand ABI here, how all of a sudden we remove a binding
>> for a hardware just because it did not get noticed until yet that as it is
>> not a real device and we always say device tree binding should not depend on
>> drivers but the device but we are saying Iris does not use fake "video-firmware"
>> device node for removal. I am a bit confused.
> 
> About what? What is unclear in standard DT ABI rules?
> 
>>
>> Whether removing will not break any ABI as initial binding enables the IRIS
>> related code to use video-firmware, now we are removing it.
>> I believe, removing binding always break ABI ? or is it depend on driver
>> code not using it ?
> 
> There is no single user of this, out of tree (I briefly checked) and
> in-tree, so there is no ABI impact. I am changing the documentation of
> the ABI, but there is no actual ABI break because impact is 0.
> 

My understanding here is that the interface "video-firmware" is already defined
in the binding. There could be possible out-of-tree users of it, might not be
possible for us to look into all of those out=of-tree users.
I support such cleanups, but also need to understand how this is not an ABI
break, just that there are no in-tree DTS user means no ABI break ?
Would appreciate if you could point to any guidelines if my understanding is not
correct, i am currently referring to [1]

[1]https://docs.kernel.org/devicetree/bindings/ABI.html

Regards,
Vikash

> I am really sorry but it seems you ask about basics of DT, so please
> first get into docs and other existing discussions.
> 
> Best regards,
> Krzysztof