On Wed, Nov 20, 2013 at 4:31 AM, Will Deacon <will.deacon@xxxxxxx> wrote: > On Tue, Nov 19, 2013 at 08:45:02PM +0000, Rob Herring wrote: >> On 11/19/2013 11:35 AM, Will Deacon wrote: >> > Adding Andreas and Rob for input on potential binding additions to the SMMU. >> >> The above proposal would be an incompatible change. However, I think we >> could still deal with a change in this binding at this stage. >> >> One way approach to handle this without changing the binding would be to >> scan the DT for all iommu's up front and create a list of all nodes and >> their iommu parent. The fact that the hierarchy is described in a way >> that doesn't fit Linux well is really a Linux implementation detail. >> >> If changing the binding, a simple approach would be to allow >> 'smmu-parent' to be a bus and/or device property and not just for >> chained iommu's. This could be a global or bus property that is >> inherited. Like interrupt-parent, you would have to deal with the parent >> being itself. Also, perhaps iommu-parent would be a better name. In any >> case, I'd like to see this all be a generic iommu binding. > > I like that idea. I've recently been toying with removing the chained IOMMU > support, since I don't think anybody is using it who is interested in > mainline. However, making it more general sounds like a better idea. > > One potential issue is that I think the nvidia guys want to describe masters > that master via multiple SMMUs (which I believe was the motivation for > moving the stream-ids out into the master nodes, rather than keeping them in > the SMMU). Again, that's not something we can easily add to the arm-smmu, > because the incoming stream-ids are a property of the SMMU node. For stream-ids, I think that is debatable. It is not a property of the SMMU. The AXI ID is determined by the master. Yes, AXI ID is only part of it and the SMMU determines the full stream-id, but that doesn't really matter. Look at interrupts properties as a comparison. The number of cells and the meaning of the cell values is determined by the interrupt controller, not the node with the interrupts property. Rob > So the question is: do we actually need to describe masters that master > through multiple SMMUs as a single node in the devicetree? > > Will -- 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
