Re: [PATCH 04/22] arm64: dts: qcom: hamoa: Reserve low IOVA range for Iris

[Dmitry Baryshkov]

On Sat, Aug 08, 2026 at 09:18:42PM +0530, Vikash Garodia wrote:
> 
> 
> On 8/7/2026 6:48 PM, Bryan O'Donoghue wrote:
> > On 07/08/2026 11:22, Vikash Garodia wrote:
> > > > > > I don't like the idea of this series, because it_again_
> > > > > > doesn't tell us
> > > > > > the truth about the hardware. This typicall ends up with
> > > > > > bigger problems
> > > > > honestly...thats all the info i have about the vpu hardware that it
> > > > > restricts non pixel to DMA from the 0-600MB range. The same i have been
> > > > > trying for a year now
> > > > You are not honest here. You also know that there are secure streams,
> > > > which have to use their own IOMMU SIDs. And some of them, as far as I
> > > > remember, also have memory range restrictions.
> > > please read the commit description again, the answer is there.
> > 
> > So I don't necessarily get all of the detail out of the commit log myself.
> > 
> > Could you give some detail to address Dmitry's point.
> > 
> > The question as I read it is - are all of the other potential SIDs
> > covered by this change ?
> > 
> 
> I get the query as "secure streams also have their dedicated reserve
> regions, so how does this approach helps" - This patch does not reserve any
> IOVA for secure streams, only the forward looking subnode can assign
> specific reserve for specific streams.
> The patch enforces a common IOVA across all streams, and is good enough to
> fix the problem we have w.r.t device reset.

No, it's not good enough. It defines that both non-secure streams use
the provided memory range, it doesn't provide a natural way to later
_expand_ it to support secure subnodes, etc.

We know that there is a problem. We already have been bitten by not
describing the hardware as is and using band-aids. Can we now learn the
lesson and write a proper hardware description?

> 
> > > > So, if we land these patches, how do extend it later to account for all
> > > > of that?
> > > > 
> > > forward looking design would be subnode, which we can land ontop of this
> > > series.
> > 
> > Yes it should be possible to branch to make subnodes work on-top of this
> > - accepting that once this lands it becomes ABI and support for this
> > method must be sustained, even after sub-nodes land.
> > 
> 
> Thats the plan. This goes as ABI with subnode to land on top of it.

So, do you actually plan to support both ABIs? This would also mean
moving reserved regions to the subnode. What prevents us from
landing subnodes straight away?

-- 
With best wishes
Dmitry