On Sat, Jul 12, 2014 at 02:22:01PM +0200, Arnd Bergmann wrote: > On Saturday 12 July 2014, Rob Clark wrote: > > >> Was there actually a good reason for having the device link to the > > >> iommu rather than the other way around? How much would people hate it > > >> if I just ignore the generic bindings and use something that works for > > >> me instead. I mean, it isn't exactly like there is going to be .dts > > >> re-use across different SoC's.. and at least with current IOMMU API > > >> some sort of of_get_named_iommu() API doesn't really make sense. > > > > > > The thing is, if you end up ignoring the generic binding then we have two > > > IOMMUs using the same (ARM SMMU) binding and it begs the question as to > > > which is the more generic! I know we're keen to get this merged, but merging > > > something that people won't use and calling it generic doesn't seem ideal > > > either. We do, however, desperately need a generic binding. > > > > yeah, ignoring the generic binding is not my first choice. I'd rather > > have something that works well for everyone. But I wasn't really sure > > if the current proposal was arbitrary, or if there are some > > conflicting requirements between different platforms. > > The common case that needs to be simple is attaching one (master) device > to an IOMMU using the shared global context for the purposes of implementing > the dma-mapping API. > > The way that Thierry's binding does that is the obvious solution to this, > and it mirrors what we do in practically every other subsystem. That wasn't really the intention, though. We shouldn't be designing bindings to work well in one use-case or another. My motivation for doing it this way was that I think it naturally models the flow of master IDs. They originate within the masters and flow towards the IOMMU device. In other words, they are a property of the masters so quite literally should be described in the device tree nodes of the masters. Thierry
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