Hi Stuart, On Mon, Jun 16, 2014 at 05:56:32PM +0100, Stuart Yoder wrote: > > Do you have use-cases where you really need to change these mappings > > dynamically? > > Yes. In the case of a PCI bus-- you may not know in advance how many > PCI devices there are until you probe the bus. We have another FSL > proprietary bus we call the "fsl-mc" bus that is similar. For that case, though, you could still describe an algorithmic transformation from RequesterID to StreamID which corresponds to a fixed mapping. > Another thing to consider-- starting with SMMUv2, as you know, there > is a new distributed architecture with multiple TBUs and a centralized > TCU that walks the SMMU page tables. So instead of sprinkling multiple > SMMUs all over an SoC you now have the option a 1 central TCU and sprinkling > multiple TBUs around. However, this means that the stream ID namespace > is now global and can be pretty limited. In the SMMU implementation we > have there are only 64 stream ID total for our Soc. But we have many more > masters than that. > > So we look at stream IDs as really corresponding to an 'isolation context' > and not to a bus master. An isolation context is the domain you are > trying to isolate with the SMMU. Devices that all belong to the same > 'isolation context' can share the same stream ID, since they share > the same domain and page tables. Ok, this is more compelling. > So, perhaps by default some/most SMMU masters may have a default stream ID > of 0x0 that is used by the host...and that could be represented > statically in the device tree. > > But, we absolutely will need to dynamically set new stream IDs > into masters when a new IOMMU 'domain' is created and devices > are added to it. All the devices in a domain will share > the same stream ID. > > So whatever we do, let's please have an architecture flexible enough > to allow for this. What is the software interface to the logic that assigns the StreamIDs? Is it part of the SMMU, or a separate device (or set of devices)? Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
