On 29/07/2019 15:08, Jose Abreu wrote: ... >>> Hi Catalin and Will, >>> >>> Sorry to add you in such a long thread but we are seeing a DMA issue >>> with stmmac driver in an ARM64 platform with IOMMU enabled. >>> >>> The issue seems to be solved when buffers allocation for DMA based >>> transfers are *not* mapped with the DMA_ATTR_SKIP_CPU_SYNC flag *OR* >>> when IOMMU is disabled. >>> >>> Notice that after transfer is done we do use >>> dma_sync_single_for_{cpu,device} and then we reuse *the same* page for >>> another transfer. >>> >>> Can you please comment on whether DMA_ATTR_SKIP_CPU_SYNC can not be used >>> in ARM64 platforms with IOMMU ? >> >> In terms of what they do, there should be no difference on arm64 between: >> >> dma_map_page(..., dir); >> ... >> dma_unmap_page(..., dir); >> >> and: >> >> dma_map_page_attrs(..., dir, DMA_ATTR_SKIP_CPU_SYNC); >> dma_sync_single_for_device(..., dir); >> ... >> dma_sync_single_for_cpu(..., dir); >> dma_unmap_page_attrs(..., dir, DMA_ATTR_SKIP_CPU_SYNC); >> >> provided that the first sync covers the whole buffer and any subsequent >> ones cover at least the parts of the buffer which may have changed. Plus >> for coherent hardware it's entirely moot either way. > > Thanks for confirming. That's indeed what stmmac is doing when buffer is > received by syncing the packet size to CPU. > >> >> Given Jon's previous findings, I would lean towards the idea that >> performing the extra (redundant) cache maintenance plus barrier in >> dma_unmap is mostly just perturbing timing in the same way as the debug >> print which also made things seem OK. > > Mikko said that Tegra186 is not coherent so we have to explicit flush > pipeline but I don't understand why sync_single() is not doing it ... > > Jon, can you please remove *all* debug prints, hacks, etc ... and test > this one in attach with plain -net tree ? So far I have just been testing on the mainline kernel branch. The issue still persists after applying this on mainline. I can test on the -net tree, but I am not sure that will make a difference. Cheers Jon -- nvpublic