On Fri, Oct 25, 2013 at 02:20:51PM +0100, Will Deacon wrote: > On Fri, Oct 25, 2013 at 09:22:02AM +0100, Hiroshi Doyu wrote: > > Thierry Reding <thierry.red...@gmail.com> wrote @ Fri, 25 Oct 2013 09:56:55 > > +0200: > > > > > I suspect that there will be enough differences between the various > > > IOMMU implementations that we won't be able to have a unified binding > > > (especially for how to associate devices with a particular virtual > > > address space), but perhaps that could be solved with something like an > > > .of_xlate() that IOMMU drivers implement, much like we've done with most > > > other subsystems too. > > > > > > The binding for Tegra's IOMMU currently only uses the HW IDs (or a mask) > > > to put a device into a given address space, but I think that could be > > > easily extended to something like: > > > > > > memory-clients = <&iommu MASK>; > > > > > > Or similar. If other information is required, we could encode that into > > > a multi-cell specifier. Perhaps we could even leave away the phandle > > > since typically there will only be a single IOMMU in the system? > > > > > > Does that sound reasonable? Hiroshi is much more familiar with IOMMUs, > > > so I'd like to get his opinion on the above as well. > > > > I think that the above may be possible, but I'd like to listen from > > other IOMMU SOC maintainers. > > > > A brief explanation for "memory-clients": > > > > In tegra, every H/W has its own memory-client ID, and it can be > > associated to any address spaces. The above "memory-cilents" is used > > to indicate which ID a device has in DT. If the other SOC IOMMUs need > > this kind of "memory-clients", this would be standarized. Any comment? > > > > At least arm-smmu seems to have the following. multiple IOMMUs can be > > handled with this. > > > > > > - smmu-parent : When multiple SMMUs are chained together, this > > property can be used to provide a phandle to the > > parent SMMU (that is the next SMMU on the path going > > from the mmu-masters towards memory) node for this > > SMMU. > > This property is for the case when IOMMUs are connected in series, which is > fairly horrendous. However, it is extremely common to have multiple IOMMU > instances within an Soc (Exynos SoCs have one IOMMU per device iirc), so > that certainly needs to be handled.
Okay, in that case perhaps some sort of generic binding should mandate the phandle, even for systems that only have a single one. I suspect a generic variant of smmu-parent (iommu-parent?) would also be useful to describe setups with cascaded IOMMUs. Thierry
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