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

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Message-ID: <4d87d1ca-55b2-426e-aa73-e3fd8c6fe7bd@kernel.org>
Date: Tue, 7 Oct 2025 15:25:29 +0100
From: Bryan O'Donoghue <bod@...nel.org>
To: Charan Teja Kalla <charan.kalla@....qualcomm.com>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Cc: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 Krzysztof Kozlowski <krzk@...nel.org>,
 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 07/10/2025 15:11, Charan Teja Kalla wrote:
> a) Keep iommus max items as 2, which is unchanged.
> b) Repeat the same sid for both entries, i.e.,
>           iommus = <&apps_smmu 0x1940 0x0000>,
>                  - <&apps_smmu 0x1947 0x0000>;
> 	        + <&apps_smmu 0x1940 0x0000>;
> 
> and then create the new device as a platform device independent of dt.
> RFC for this is posted[1].

If you are going to bury iommu data into the platform code in the 
driver, why do you need to modify this array at all ?

The upstream DT should describe what is correct for the APSS - Linux.

There's nothing to stop having an exotic set of platform code in drivers 
to setup SMMU entries for non-APSS system agents though.

Seems a shame though - in the ideal the DT should describe the whole 
hardware and the FUNCTION_ID would be included into the iommu entries.

Rob suggested using an implicit index for function id

https://lore.kernel.org/all/CAL_JsqK9waZK=i+ov0jV-PonWSfddwHvE94Q+pks4zAEtKc+yg@mail.gmail.com/

Couldn't we list the entire set of iommus - then detach - subsequently 
re-attaching in our platform code with FUNCTION_IDs we keep listed in 
our drivers ?

That way the DT is complete and correct, we have a compliant upstream DT 
but we also find a way to make the FUNCTION_ID specific setup we need.

---
bod