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

[Dmitry Baryshkov]

On Thu, Aug 06, 2026 at 11:11:09AM +0200, Krzysztof Kozlowski wrote:
> 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.

But there are no separate addresses for those subnodes. Would you prefer
them to duplicate the addresses of the parent node? Or would the
'ranges' be enough?

Or, thinking about it, if Venus / Iris have 32-bit addressing, then
dma-range should probably define the limited DMA range.

-- 
With best wishes
Dmitry