> 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. Cheers, Jérôme
