On 18/04/17 02:31 PM, Dan Williams wrote: > On Tue, Apr 18, 2017 at 1:29 PM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >>> On Tue, Apr 18, 2017 at 12:35 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx> >>> wrote: >>>> >>>> >>>> On 18/04/17 01:01 PM, Jason Gunthorpe wrote: >>>>> Ultimately every dma_ops will need special code to support P2P with >>>>> the special hardware that ops is controlling, so it makes some sense >>>>> to start by pushing the check down there in the first place. This >>>>> advice is partially motivated by how dma_map_sg is just a small >>>>> wrapper around the function pointer call... >>>> >>>> Yes, I noticed this problem too and that makes sense. It just means >>>> every dma_ops will probably need to be modified to either support p2p >>>> pages or fail on them. Though, the only real difficulty there is that it >>>> will be a lot of work. >>> >>> I don't think you need to go touch all dma_ops, I think you can just >>> arrange for devices that are going to do dma to get redirected to a >>> p2p aware provider of operations that overrides the system default >>> dma_ops. I.e. just touch get_dma_ops(). >> >> This would not work well for everyone, for instance on GPU we usualy >> have buffer object with a mix of device memory and regular system >> memory but call dma sg map once for the list. >> > > ...and that dma_map goes through get_dma_ops(), so I don't see the conflict? The main conflict is in dma_map_sg which only does get_dma_ops once but the sg may contain memory of different types. Logan
