On Thu, Oct 01, 2015 at 07:30:28PM +0200, Gerald Schaefer wrote: > Yes, the DMA API is already implemented in arch/s390/pci/pci_dma.c. > I thought about moving it over to the new location in drivers/iommu/, > but I don't see any benefit from it. Okay, this is true for now. At some point we hopefully have a common DMA-API implementation for all IOMMU driver, at which point s390 can make use of it too and abandon its own implementation. > Also, the two APIs are quite different on s390 and must not be mixed-up. > For example, we have optimizations in the DMA API to reduce TLB flushes > based on iommu bitmap wrap-around, which is not possible for the map/unmap > logic in the IOMMU API. There is also the requirement that each device has > its own DMA page table (not shared), which is important for DMA API device > recovery and map/unmap on s390. This sounds quite similar to what other IOMMU drivers also implement, especially the AMD IOMMU driver. It also uses non-shared page-tables for devices and implements the bitmap-allocator optimization. > Hmm, not sure how this can replace my own struct. I need the struct to > maintain a list of all devices that share a dma page table. And the > devices need to be added and removed to/from that list in attach/detach_dev. > > I also need that list during map/unmap, in order to do a TLB flush for > all affected devices, and this happens under a spin lock. > > So I guess I cannot use the iommu_group->devices list, which is managed > in add/remove_device and under a mutex, if that was on your mind. Yeah, right. Thanks for the explanation. Joerg -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
