On Thu, Mar 29, 2018 at 10:25:52AM -0600, Logan Gunthorpe wrote: > > > On 29/03/18 10:10 AM, Christian König wrote: > > Why not? I mean the dma_map_resource() function is for P2P while other > > dma_map_* functions are only for system memory. > > Oh, hmm, I wasn't aware dma_map_resource was exclusively for mapping > P2P. Though it's a bit odd seeing we've been working under the > assumption that PCI P2P is different as it has to translate the PCI bus > address. Where as P2P for devices on other buses is a big unknown. dma_map_resource() is the right API (thought its current implementation is fill with x86 assumptions). So i would argue that arch can decide to implement it or simply return dma error address which trigger fallback path into the caller (at least for GPU drivers). SG variant can be added on top. dma_map_resource() is the right API because it has all the necessary informations. It use the CPU physical address as the common address "language" with CPU physical address of PCIE bar to map to another device you can find the corresponding bus address from the IOMMU code (NOP on x86). So dma_map_resource() knows both the source device which export its PCIE bar and the destination devices. So i don't think Christian need to base his patchset on yours. This is orthogonal. Christian is using existing upstream API, if it is broken on some arch it is up to those arch to fix it, or return error if it is not fixable. In fact i would assume that you would need to base your patchset on top of dma_map_resource() too ... Moreover i doubt Christian want to have struct page for this. For nouveau there will be HMM struct page and this would conflict. AFAICT you need struct page because the API you are trying to expose to user space rely on "regular" filesystem/RDMA umem API which all assume struct page. GPU drivers do not have this requirement and it should not be impose on them. So from my point of view Christian patchset is good as it is. Modulo better commit message. Bottom line i think we need common PCIE helper for P2P and the current dma_map_resource() is the right kind from POV. What you are doing with struct page is specific to your sub-system and should not be impose on others. Cheers, Jérôme
