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?
