Subject: Re: [PATCH v15 0/3] of: parsing of multi #{iommu,msi}-cells in maps

From: Krzysztof Kozlowski <[email-masked]>
Date: Tue, 26 May 2026 08:12:26 +0200

On Wed, May 20, 2026 at 01:32:39PM +0530, Vijayanand Jitta wrote:
> So far our parsing of {iommu,msi}-map properties has always blindly
> assumed that the output specifiers will always have exactly 1 cell.
> This typically does happen to be the case, but is not actually enforced
> (and the PCI msi-map binding even explicitly states support for 0 or 1
> cells) - as a result we've now ended up with dodgy DTs out in the field
> which depend on this behaviour to map a 1-cell specifier for a 2-cell
> provider, despite that being bogus per the bindings themselves.
> 
> Since there is some potential use[1] in being able to map at least
> single input IDs to multi-cell output specifiers (and properly support
> 0-cell outputs as well), add support for properly parsing and using the
> target nodes' #cells values, albeit with the unfortunate complication of
> still having to work around expectations of the old behaviour too.
> 							-- Robin.
> 
> Unlike single #{}-cell, it is complex to establish a linear relation
> between input 'id' and output specifier for multi-cell properties, thus
> it is always expected that len never going to be > 1.
> 
> These changes have been tested on QEMU for the arm64 architecture.

So there is no real user for that. That's unconvincing. I would assume
that at least you have real user where you test it.

If you want to speed up acceptance of your patches, then also I would
prefer to see at least one more user, beside Qualcomm. IOW, show how you
solve other people problems, not only yours.

Best regards,
Krzysztof