linux-kernel - Re: [PATCH v3 0/5] Introduce "non-pixel" sub node within iris video node

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Message-ID: <6ead45a6-aac8-464d-9812-f5e0d1395709@oss.qualcomm.com>
Date: Thu, 9 Oct 2025 10:53:30 +0530
From: Charan Teja Kalla <charan.kalla@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Bryan O'Donoghue <bod@...nel.org>,
        Bryan O'Donoghue <bod.linux@...w.ie>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Vikash Garodia <quic_vgarodia@...cinc.com>,
        Dikshita Agarwal <quic_dikshita@...cinc.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>, linux-media@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/5] Introduce "non-pixel" sub node within iris video
 node



On 10/9/2025 6:02 AM, Krzysztof Kozlowski wrote:
>> If it is legitimate meta-data for the SMMU setup then why _shouldn't_ it 
>> go into the DT ?
>>
> We talked about this two or three months ago. I don't understand why you
> just ignored that entire part and come with new binding just to not
> touch iommu code. List of entries in iommu must have strict order, just
> like for every other list, and you should rely on that.
Hi Krzysztof,

I want to understand a bit more about the statement -- "List of entries
in iommu must have strict order."

per my understanding:
iommus = <&apps_smmu sid1 mask1>, <&apps_smmu sid2 mask2>;

     and

iommus = <&apps_smmu sid2 mask2>, <&apps_smmu sid1 mask1>;

The end result is same with no breakage as they still end up in using
the same translation unit, i.e., ordering doesn't matter.

May be you imply something else(may be ABI[1]) here about the order,
which I am unable to catch...

[1]
https://lore.kernel.org/linux-media/8b88cea4-b9f2-4365-829c-2a255aed6c69@kernel.org/