Thierry Reding <thierry.reding@xxxxxxxxx> 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.
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