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

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Message-ID: <a3325bf1-2a3f-416a-ba2a-4fb1e9f85e61@linaro.org>
Date: Mon, 25 Aug 2025 14:02:56 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
Cc: Vikash Garodia <quic_vgarodia@...cinc.com>,
 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 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.

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