linux-kernel - Re: [PATCH v3 1/5] media: dt-bindings: add non-pixel property in iris schema

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Message-ID: <1cc6f462-dfd2-46ed-8534-a44812ef1cbd@kernel.org>
Date: Wed, 2 Jul 2025 14:11:35 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: 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>
Cc: linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] media: dt-bindings: add non-pixel property in iris
 schema

On 02/07/2025 14:08, Vikash Garodia wrote:
> 
> On 7/2/2025 5:28 PM, Krzysztof Kozlowski wrote:
>> On 02/07/2025 13:55, Vikash Garodia wrote:
>>>
>>>
>>> On 7/2/2025 5:17 PM, Krzysztof Kozlowski wrote:
>>>> On 02/07/2025 13:45, Vikash Garodia wrote:
>>>>>
>>>>> On 7/2/2025 4:53 PM, Krzysztof Kozlowski wrote:
>>>>>> On 27/06/2025 17:48, Vikash Garodia wrote:
>>>>>>> +
>>>>>>>      video-codec@...0000 {
>>>>>>>          compatible = "qcom,sm8550-iris";
>>>>>>>          reg = <0x0aa00000 0xf0000>;
>>>>>>> @@ -144,12 +176,16 @@ examples:
>>>>>>>          resets = <&gcc GCC_VIDEO_AXI0_CLK_ARES>;
>>>>>>>          reset-names = "bus";
>>>>>>>  
>>>>>>> -        iommus = <&apps_smmu 0x1940 0x0000>,
>>>>>>> -                 <&apps_smmu 0x1947 0x0000>;
>>>>>>> +        iommus = <&apps_smmu 0x1947 0x0000>;
>>>>>>
>>>>>> I missed, that's technically ABI break and nothing in commit msg
>>>>>> explains that. You need to clearly explain the reasons and impact.
>>>>> No, it is not. Interface works well with old or new approach.
>>>>
>>>>
>>>> You changed the order of IOMMUs, so yes it is. Which interface works
>>>> well - FreeBSD? Or other? You are changing ABI for every user.
>>> Why do i need to change, when without changing would work as well ?
>> ? I don't understand. I made a statement, not a question. You are doing
>> this - you are changing the ABI.
>>
>> Which item was the first IOMMU before and which was second?
>>
>> Which item is the first IOMMU now?
> Old approach - max 2 iommus interface - <SID-A, SID-B>
> New approach - min 1/max 2, iommu interface - <SID-B>, child - <SID-A>

So you changed first IOMMU entry, first IOMMU master and that is
technically ABI break.

> 
> If both works, how is interchanging impacting any existing hardware OR breaking
> ABI ?

Because you change the entries. The ordering of lists - not iommus which
do not matter for Linux here - was discussed many times, so just refer
to that discussions.



Best regards,
Krzysztof