Re: [PATCH 2/2] arm64: dts: qcom: hamoa: Reserve low IOVA range for Iris

[Vikash Garodia]

On 6/2/2026 9:05 PM, Daniel J Blueman wrote:
> On Tue, 2 Jun 2026 at 18:27, Bryan O'Donoghue <bod@xxxxxxxxxx> wrote:
> > On 01/06/2026 05:13, Daniel J Blueman wrote:
> > > On X1-family hamoa platforms, Iris DMA below IOVA 0x25800000 (600MB)
> > > triggers unhandled SMMU page faults
> >
> > How do we know that is a correct address - does it come from qcom
> > documentation or trial and error ?
>
> @Vikash, beyond your comment I linked in the patch [1] kindly cite a
> source for the different stream-ID <600MB behaviour, and share
> specifics, eg if silicon, firmware, or driver and constraint, defect
> or otherwise, so I can include a definitive description.
>
> Also good to know if my workaround is good for long-term, or on the
> other hand handling streams <600MB is important/useful.

Thanks Daniel for raising this patch. Did you also try the memory fix i 
mentioned in the bug [1] discussion ?

Coming to 600MB, this have been the VPU hardware restriction all the 
while since venus days, and since address could not go deeper all the 
way lower than 600MB, the issue never popped up earlier.

Consider the memory layout split as below (Iris device range is capped 
to 0xe0000000)

|-----600MB-----|-----(0xe0000000 - 600MB)-----|----IO reg--|

0-600MB range, VPU hardware would reserve this to generate different 
stream-IDs primarily for internal (non-pixel) buffers.

0-600 --> VPU would generate *secure* stream ID for non-pixel buffers
601 - 0xe0000000 --> VPU would generate non-secure stream ID for 
non-pixel buffers.

When many concurrent sessions were tried, non-pixel buffers were mapped 
into 0-600MB range, and VPU generated secure ID for those. Since those 
were not associated with the iommus configured for iris node, it led to 
USF (un-identified stream fault) and device would crash.

Keeping the region reserved, makes the non-pixel buffer always in the 
non secure range (601-..) and avoids the crash.

Downside of this design - It would eventually reserve 0-600MB un-map 
'able for all buffer types, like pixel as well which do not have any 
such restriction.

Forward looking design - create devices dynamically and set reserve 
regions for those specific device using the api [1], instead of applying 
one reserve for all.

[1] 
https://lore.kernel.org/all/20260119054936.3350128-1-busanna.reddy@xxxxxxxxxxxxxxxx/ 


> Thanks,
>    Dan
>
> [1] https://github.com/qualcomm-linux/kernel-topics/issues/1157#issuecomment-4458933574
>
> --
> Daniel J Blueman