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

Dmitry Baryshkov
2025-10-08T03:11:38Z

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