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

On 8/12/2026 6:16 PM, Dmitry Baryshkov wrote:
> On Wed, Aug 12, 2026 at 06:02:58AM +0100, Bryan O'Donoghue wrote:
>> On 10/08/2026 17:57, Vikash Garodia wrote:
>>>
>>>
>>> On 8/10/2026 5:40 PM, Dmitry Baryshkov wrote:
>>>> 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.
>>>
>>> How is that different from moving the reserve region when stream IDs
>>> would also need to move, so be it for the associated memory regions.
>>>
>>>> What prevents us from landing subnodes straight away?
>>>>
>>>
>>> You are well aware of them, but still asking the same. Reasons,
>>> 1. We have been attempting the subnodes for almost a year with multiple
>>> pushbacks from multiple maintainers. We are closer and working on it to
>>> post for iris, followed by venus, once review is acceptable for iris.
>>> 2. Current solution, in this series, is much easy to apply for all
>>> kernels and can land faster so that it can fix the reset issue we have
>>> for already enabled devices.
>>>
>>> Both from timewise and simplicity wise, this proposal is made to address
>>> the reset issue, while subnode can land ontop of this, without breaking ABI.
>>>
>>> Regards,
>>> Vikash
>>>
>>
>> There is another solution.
>>
>> Restrict multiple concurrent streams in both drivers. The failure mode is as
>> I understand it only triggered by _concurrent_ streams so, restrict that
>> case in the .c code.
> 
> I think this might be the best hot fix for now. Very local, very

No, it's not. Restricting concurrency does not avoid the reset, it just 
reduces the possibility of occurrence.

> presice, touching the driver pieces, letting it to continue to exist
> even after the subnodes have landed to support the legacy case.
>