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

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Message-ID: <1516f21e-aee3-42cf-b75e-61142dc9578d@oss.qualcomm.com>
Date: Wed, 8 Oct 2025 23:33:17 +0530
From: Charan Teja Kalla <charan.kalla@....qualcomm.com>
To: Bryan O'Donoghue <bod@...nel.org>, Bryan O'Donoghue <bod.linux@...w.ie>,
        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 10/7/2025 8:14 PM, Bryan O'Donoghue wrote:
> On 07/10/2025 15:29, Bryan O'Donoghue wrote:
>> On 07/10/2025 15:25, Bryan O'Donoghue wrote:
>>> Rob suggested using an implicit index for function id
>>>
>>> https://lore.kernel.org/all/CAL_JsqK9waZK=i+ov0jV-
>>> PonWSfddwHvE94Q+pks4zAEtKc+yg@...l.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 ?
>>>

TMK, there is no api exist to detach a device once it is attached to
smmu. We used to have one but removed[1], not sure how well it will be
received to introduce it again.

There is other problem exist attaching the entire set of iommus in the
first place: Usually writes to SMR registers are protected through
emulation by hyp. Thus adding the sids of protected/non-protected
usecases in the same iommu set will not allowed by the
hypervisors(eg:gunyah), as all will end up in using the same context
bank, thus there can be failure to attach to smmu in the first place.


[1]
https://lore.kernel.org/all/20230110025408.667767-1-baolu.lu@linux.intel.com/

>>> 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.
>>
>> i.e. you can keep the FUNCTION_ID "metadata" in the driver and
>> associate specific iommu indexes with the FUNCTION_ID you want in there.
>>
>> That way you could have multiple FUNCTION_ID smmu entries in the DT
>> and just associate the DT indexes locally in drivers/platform/qcom/
>> iris_metadata_goes_here.c
>>
>> ---
>> bod
> 
> Actually why can't we specify FUNCTION_ID in the iommus = <entries>
> 
> Surely we could do
> 
>     #iommu-cells = <4>;
>     iommus = <&apps_smmu 0x420 0x2 FUNCTION_ID>;
> 
> and encode the real data we need directly in the iommus list...
> 

Since it is the smmu device property , this suggestion expects all the
devices, not just video, to define additional argument. Does this look
valid?

> ---
> bod