On Tue, Feb 03, 2015 at 11:22:01AM -0500, Rob Clark wrote: > On Tue, Feb 3, 2015 at 11:12 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > I agree for the case you are describing here. From what I understood > > from Rob was that he is looking at something more like: > > > > Fig 3 > > CPU--L1cache--L2cache--Memory--IOMMU---<iobus>--device > > > > where the IOMMU controls one or more contexts per device, and is > > shared across GPU and non-GPU devices. Here, we need to use the > > dmap-mapping interface to set up the IO page table for any device > > that is unable to address all of system RAM, and we can use it > > for purposes like isolation of the devices. There are also cases > > where using the IOMMU is not optional. > > > Actually, just to clarify, the IOMMU instance is specific to the GPU.. > not shared with other devices. Otherwise managing multiple contexts > would go quite badly.. > > But other devices have their own instance of the same IOMMU.. so same > driver could be used. Okay, so that is my Fig.2 case, and we don't have to worry about Fig.3. One thing I forgot in Fig.1/2 which my original did have were to mark the system MMU as optional. (Think an ARM64 with SMMU into a 32-bit peripheral bus.) Do we support stacked MMUs in the DMA API? We may need to if we keep IOMMUs in the DMA API. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>