Re: [PATCH v2 01/12] dt-bindings: media: qcom,venus: Add context bank subnodes to common schema

[Krzysztof Kozlowski]

On 06/08/2026 10:46, Dmitry Baryshkov wrote:
> 
>> dma-ranges tell how this bus - so venus/iris - performs DMA translation
>> in respective to parent. Address/size-cells are obviously also needed if
>> this is a bus with addressing.
>>
>> But there are no children with addressing, thus what sort of bus would
>> it be?
>>
>> It looks to me that having here both:
>> 1. dma-ranges + address/size-cells
>> 2. children without bus addressing
>> is some sort of abuse of the DT syntax. It is allowed, but does not
>> really represent hardware.
>>
>> IOW, dma-ranges alone feels okay, although unusual, and it states proper
>> DMA translation for this bus. If you add address/size-cells, it means
>> this bus HAS addressing and thus YOU MUST use addressing.
>>
>> If my understanding is correct, then solution would be to add addressing
>> to the children (so unit address and "reg" property) or drop
>> address/size-cells as Rob pointed out. [1]
> 
> Doesn't dma-ranges require address/size cells? In the end, how can you

I think it does not require, at least how I understood the DT spec,
unless you provide actual addresses to the property.

IOW, this requires address/size-cells:
	dma-ranges = <0 0 0 0 0x10 0>;

> specify the DMA address if the device doesn't have addressing at all (or
> MMIO-style addressing)?

Yeah, that's why having here children without bus addressing is
confusing. I would interpret it that, children are not on MMIO bus, thus
the venus/iris is some sort of proprietary bus with no mapping between
parent MMIO and children nodes.

If there is no mapping, then we do not have 'ranges' property. But I
could imagine that such no-mapping bus still provides access to system RAM?

Actually this feels like a huge stretch, so I tend to think that the
only reasonable option is to have children with MMIO, which would make
it explicit: Venus/iris is a bus which provides translation of both MMIO
and DMA addresses to the parent.


Best regards,
Krzysztof