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

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Message-ID: <ogslvjglnz56lz6nria7py6i4ccp6zvcd4ujpiusrq6xutydsm@xb72os5wk67r>
Date: Wed, 8 Oct 2025 06:11:32 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Vikash Garodia <quic_vgarodia@...cinc.com>
Cc: Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        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 Sat, Jul 05, 2025 at 12:45:10AM +0530, Vikash Garodia wrote:
> 
> On 7/4/2025 1:53 PM, Bryan O'Donoghue wrote:
> > On 03/07/2025 22:23, Dmitry Baryshkov wrote:
> >>> I still give my RB for the series.
> >>>
> >>> To me the only question is should it be applied to sm8550 or to new SoCs
> >>> from now on, sa8775p, x1e and derivatives.
> >> I think we need to apply it to_all_ SoCs, maybe starting from MSM8x26
> >> and MSM8x16. Likewise, we need to think bout secure buffers usecase. And
> >> once we do that, we will realize that it also changes the ABI for all
> >> SoCs that support either Venus or Iris.
> > 
> > I think a dts change is a non-starter as its an ABI break.
> > 
> > So if ABI break is out and reworking future dts to allow for a new device is
> > out, then some API change is needed to allow the driver to stop the kernel
> > automatically setting up the IOMMUs, create the new device as a platform device
> > not dependent on DT change and have the probe() of the relevant drivers setup
> > their own IOMMU extents based on - probably indexes we have in the driver
> > configuration parameters.
> 
> The concept of sub device is nothing new, it has been there for firmware iommus
> on venus bindings [1] and i am just extending it for non-pixel on iris. So
> instead of complicating the driver, pls relook into the existing solution which
> looks much simpler.

We should not be using sub-devices. They don't describe any actual block
or device in the hardware, as such they are frowned upon by DT bindings
maintainers.

> 
> The proposal to dis-associate from DT would certainly bite us in future when we
> have more and more iommu configurations, lets say "qcom,iommu-vmid" [2], comes
> in for managing secure stream-ids.
> 
> [1]
> https://elixir.bootlin.com/linux/v6.16-rc4/source/Documentation/devicetree/bindings/media/qcom,venus-common.yaml#L50
> 
> [2] https://lore.kernel.org/all/20231101071144.16309-2-quic_gkohli@quicinc.com/

-- 
With best wishes
Dmitry