On 07.05.2018 10:59, Joerg Roedel wrote: > On Fri, Apr 27, 2018 at 12:02:02PM +0200, Thierry Reding wrote: >> Joerg, I've gone over the git log and header files and I see no mention >> of why the TLB flush interface isn't used for mapping. Do you recall any >> special reasons why the same shouldn't be applied for mapping? Would you >> accept any patches doing this? > > Yeah, the reason was that we assumed that only emulated IOMMUs ever need > flushing in the mapping path, and there is no reason to optimize for > that. Especially when a call to iotlb_sync() in the mapping path would > hurt most other users. > > Does the tegra-gart actually need it too?
Tegra-GART is exactly an emulated IOMMU, it doesn't have anything like TLB and it's simply a remapping table. What is actually needed for the GART - is to make sure that the remapping table modifications reach GART HW before anything tries to touch the modified page entries. Presumable there is some kind of a HW buffer that accumulates multiple registers writes and issues them in bursts to improve performance, read-after-write is the way to flush that buffer. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
