Re: [PATCH 3/7] of/iommu: add multi-map support

[Robin Murphy]

On 2026-01-27 11:45 am, Dmitry Baryshkov wrote:
> On Mon, Jan 26, 2026 at 05:55:46PM +0530, Vikash Garodia wrote:
> > From: Charan Teja Kalla <charan.kalla@xxxxxxxxxxxxxxxx>
> >
> > When multiple mappings are present for an input id, linux matches just
> > the first one. There is a usecase[1] where all the mappings are to be
> > maintained in parallel for an iommu-map entry of a same input id.
>
> This contradicts the IOMMU idealogy (at least as far as I understood it
> fom the maintainers): the device (driver) doesn't control which IOMMUs
> are getting used. Instead _all_ defined entries should get used. For
> iommu-map it means that if the map defines several entries for a single
> function, then all entries should always get mapped.

Indeed there is no concept of "multi-map" - if a single input ID 
represents more than one thing then that notion of "input ID" is 
fundamentally wrong. A single *device* may have multiple IDs, as in the 
case of PCI bridge aliasing, but in that case there are multiple things 
to map.

Thanks,
Robin.