On Wed, Jan 30, 2019 at 02:22:34PM -0500, Jerome Glisse wrote: > For GPU it would not work, GPU might want to use main memory (because > it is running out of BAR space) it is a lot easier if the p2p_map > callback calls the right dma map function (for page or io) rather than > having to define some format that would pass down the information. This is already sort of built into the sgl, you are supposed to use is_pci_p2pdma_page() and pci_p2pdma_map_sg() and somehow it is supposed to work out - but I think this is also fairly incomplete. ie the current APIs seem to assume the SGL is homogeneous :( > > Worry about optimizing away the struct page overhead later? > > Struct page do not fit well for GPU as the BAR address can be reprogram > to point to any page inside the device memory (think 256M BAR versus > 16GB device memory). The struct page only points to the BAR - it is not related to the actual GPU memory in any way. The struct page is just an alternative way to specify the physical address of the BAR page. I think this boils down to one call to setup the entire BAR, like nvme does, and then using the struct page in the p2p_map SGL?? Jason
