> -----Original Message----- > From: Will Deacon [mailto:will.deacon@xxxxxxx] > Sent: Monday, June 16, 2014 12:04 PM > To: Yoder Stuart-B08248 > Cc: Sethi Varun-B16395; Thierry Reding; Mark Rutland; > devicetree@xxxxxxxxxxxxxxx; linux-samsung-soc@xxxxxxxxxxxxxxx; Pawel > Moll; Arnd Bergmann; Ian Campbell; Grant Grundler; Stephen Warren; linux- > kernel@xxxxxxxxxxxxxxx; Marc Zyngier; Linux IOMMU; Rob Herring; Kumar > Gala; linux-tegra@xxxxxxxxxxxxxxx; Cho KyongHo; Dave P Martin; linux-arm- > kernel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree > bindings > > 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)? For us at the hardware level there are a few different ways that the streamIDs can be set. It is not part of the SMMU. In the cases where there is simply 1 device to 1 streamID (e.g. USB controller) there is an SoC register where you just program the stream ID. In the case of PCI, our PCI controller has a RequesterID-to-streamID table that you set via some PCI controller registers. The way we generally thought it would work was something like this: -u-boot/bootloader makes any static streamID allocation if needed, sets a default streamID (e.g. 0x0) in device and expresses that in the device tree -device tree would express relationship between devices (including bus controllers) and the SMMU through mmu-masters property -u-boot would express the range of unused (or used) streamIDs via a new device tree property so the kernel SMMU driver knows what streamIDs are free -in the SMMU driver a different vendor specific 'add_device' callback could be used to handle our special cases where we need to set/change the stream ID for devices added to a domain Thanks, Stuart -- 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
