Re: [RFC PATCH 07/11] arm64: dts: qcom: hamoa: Move Iris IOMMUs to sub nodes

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

On 09/07/2026 13:35, Vikash Garodia wrote:
> The Iris VPU has separate streams with different IOVA constraints. The
> non-pixel stream must be limited to the 0-600 MB IOVA range, while the
> pixel stream can use the full IOVA space.


> Using a single set of IOMMU entries for the Iris node does not describe
> these per-stream limits and can allow accesses outside the supported
> range, which may lead to device crashes. One such issue was reported at:
> https://gitlab.freedesktop.org/drm/msm/-/work_items/100
> 
> Add non-pixel and pixel child nodes, move each stream ID to its
> corresponding child node, and add a reserved IOVA range for the
> non-pixel stream.
> 
> Co-developed-by: Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
> Signed-off-by: Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
> Signed-off-by: Vikash Garodia <vikash.garodia@oss.qualcomm.com>
The thing of it is, this _is_ a bugfix - perhaps its not one that can be 
backported, actually scratch that, this isn't possible to land in 
-stable realistically.

So what is needed here is a strategy for fixing -stable.

That could be apply Daniel's patch and backport it with Fixes: - with 
mainline then say applying this change and reverting Daniel's patch

or

That could mean some other solution for -stable - up for debate - what's 
not up for debate is this series needs to _address_ what happens to 
stable for all of the target platforms - and then transition mainline to 
the new and shiny way.

That could mean

- Applying Daniel's fix with Fixes: and cc-stable
- That patch needs to be extended to _each_ Iris platform containing
   this bug... all of them I think.
- Updating bindings
- Updating DT with new method simultaneously reverting Daniel's fix

And I do mean doing that in one progressive series - a fixup for 
mainline alone isn't enough.

So we backport a fix from mainline and then make mainline better still. 
Or whatever something like that.

Either way just fixing in mainline is not good enough for each of the 
targeted upstream DTS we need a solution for -stable too, keeping in 
mind new kernels need to work with old bindings.

---
bod