On Tue, 2011-05-17 at 11:31 +0200, Alexander Graf wrote: > On 17.05.2011, at 11:11, Benjamin Herrenschmidt wrote: > > > On Tue, 2011-05-17 at 10:01 +0200, Alexander Graf wrote: > >> I'm not sure I fully understand how this is supposed to work. If the > >> tables are kept inside the kernel, how does userspace get to know > >> where to DMA to? > > > > The guest gets a dma range from the device-tree which is the range of > > device-side dma addresses it can use that correspond to the table. > > > > The guest kernel uses the normal linux iommu space allocator to allocate > > space in that region and uses H_PUT_TCE to populate the corresponding > > table entries. > > > > This is the same interface that is used for "real" iommu's with PCI > > devices btw. > > I'm still slightly puzzled here :). IIUC the main point of an IOMMU is for > the kernel > to change where device accesses actually go to. So device DMAs address A, > goes through > the IOMMU, in reality accesses address B.
Right :-) > Now, how do we tell the devices implemented in qemu that they're supposed to > DMA to > address B instead of A if the mapping table is kept in-kernel? Oh, bcs qemu mmaps the table :-) Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
