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

On 8/18/2026 11:53 AM, Dmitry Baryshkov wrote:
> On Mon, Aug 17, 2026 at 10:54:47AM +0100, Bryan O'Donoghue wrote:
>> On 10/08/2026 14:47, Rob Herring wrote:
>>>>> As per the reserved-memory.yaml schema document, the iommu-addresses
>>>>> property for IOVA reservation into /reserved-memory is allowed — it's
>>>>> documented for IOVA carveout reservations:
>>>>> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/
>>>>> schemas/reserved-memory/reserved-memory.yaml#L56
>>>> I think that is an entirely reasonable reading of the text
>>>>
>>>> Quote:
>>>>
>>>> "If no "reg" property is specified, the "iommu-addresses" property
>>>>     defines carveout regions in the IOVA space for the given device. This
>>>>     can be useful if a certain memory region should not be mapped through
>>>>     the IOMMU."
>>>>
>>>> Which is exactly what this series does. Excludes a specific IOVA range
>>>> from being allocated for this device.
>>> But if "iommu-addresses" is the only property of the reserved memory,
>>> why put this property in reserved-memory rather than directly in the
>>> device's node? I'm only questioning where is the right place to
>>> describe a reserved IOVA.
>>>
>>> Rob
>>
>> Back from the eclipse, sorry for the delayed response.
>>
>> Ah I get you.
>>
>> Yes.
>>
>> I take your point. This is a property of the node itself; the IOVA < 600MB
>> only matters _if_ the venus or iris nodes are enabled - otherwise an IOVA <
>> 600MB is perfectly fine.
>>
>> So it follows its a property specific to this node not specific to the
>> overall system.
>>
>> Yep, I agree - its a device/node property, not a top-level property.
> 
> :-)
> 
> FWIW, I think it's a proper way to describe it too.
> 

 From my readings, a node defined under reserved-memory can have other 
properties like "reg" alongwith "iommu-addresses". Are we saying when 
*only* "iommu-addresses" is there, then move to the device and when 
other property is there, then move to individual device ?

Again the device may have the "reg" property already, in such case, 
moving the iommu-addresses + reg in corresponding device might not be 
feasible.

Regards,
Vikash