On 10/25/2013 07:20 AM, Will Deacon wrote: > On Fri, Oct 25, 2013 at 09:22:02AM +0100, Hiroshi Doyu wrote: >> 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. > > 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. That property sounds a bit scary; is the value a single parent IOMMU? What if an IOMMU splits its requests between two different parent IOMMUs based on some property of the request. I hope smmu-parent isn't going to get us into another interrupts -vs- interrupts-extended situation. (/me checks the documentation of that property) I suppose smmu-parent is documented in a device-specific binding rather than as a generic property, although there's no vendor-prefix on the property name:-(, so we havne't cornered ourselves too much here; any IOMMU device which actually has multiple parents can always define its own custom property to represent that. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
