Re: [RFC PATCH 00/11] : media: iris: Migrate iommus to iris sub nodes

[Vikash Garodia]

On 7/10/2026 4:05 PM, Bryan O'Donoghue wrote:
> On 09/07/2026 13:35, Vikash Garodia wrote:
> > Mapping a stream outside its expected range can cause unintended
> > behavior, including device crashes, as reported at:
> > https://gitlab.freedesktop.org/drm/msm/-/work_items/100
> >
> > Daniel, who reported the crash issue, have also raised a patch to 
> > workaround
> > the issue. While the patch partially handles the limitation, it is 
> > inefficient
> > in a way that it keep iris hardwares away from using the 600MB address 
> > space
> > for all the different streams.
> >
> > To address this limitation, the subset of stream/s are now represented as
> > sub nodes, so that they can be associated to the respective addressable
> > range.
> > In the past, this limitation was tried with iommu-map approach, with iris
> > driver dynamically creating the devices. The approach was later concluded
> > as an hack to avoid having sub nodes. It was discussed in detail in the
> > discussionhttps://lore.kernel.org/all/c7b956a9-d3e8-4e18- 
> > b780-5d08f5cd2ca1@xxxxxxxxxx/
> >
> > It was agreed by maintainers to proceed with sub node approach to address
> > the VPU hardware limitation.
>
> What's the addressable range with sub-nodes ?
>
> The original problem you were trying to solve was the total addressable 
> size - this other problem here segmenting the linear allocation space is 
> adjacent but not the same thing.
>
> Without digging through all of the patches here - my question is does 
> the original sub-node addressable space problem get resolved in your 
> proposal here ?

The proposal solves both the problem we have so far - total addressable 
size as well as which segment (or range) in that is _not_ addressable.

Regards,
Vikash

> ---
> bod