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

[Bryan O'Donoghue <bod@kernel.org>]

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@kernel.org/
> 
> 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 ?

---
bod