On Tue, 23 Sep 2025 14:43:33 -0300 Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Tue, Sep 23, 2025 at 11:30:41AM -0600, Alex Williamson wrote: > > On Tue, 23 Sep 2025 12:04:14 -0300 > > Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > > > > > On Mon, Sep 22, 2025 at 03:00:32PM -0600, Alex Williamson wrote: > > > > But then later in patch 8/ and again in 10/ why exactly do we cache > > > > the provider on the vfio_pci_core_device rather than ask for it on > > > > demand from the p2pdma? > > > > > > It makes the most sense if the P2P is activated once during probe(), > > > it is just a cheap memory allocation, so no reason not to. > > > > > > If you try to do it on-demand then it will require more locking. > > > > I'm only wondering about splitting to an "initialize/setup" function > > where providers for each BAR are setup, and a "get provider" interface, > > which doesn't really seem to be a hot path anyway. Batching could > > still be done to setup all BAR providers at once. > > I agree it is a weird interface, but it is close to the existing weird > interface :\ Seems like it would help if we just positioned it as a "get provider for BAR" function that happens to initialize all the providers on the first call, rather than an "enable" function with some strange BAR argument and provider return. pcim_p2pdma_provider(pdev, bar)? It would at least make sense to me then to store the provider on the vfio_pci_dma_buf object at the time of the get feature call rather than vfio_pci_core_init_dev() though. That would eliminate patch 08/ and the inline #ifdefs. > > However, the setup isn't really once per probe(), even in the case of a > > new driver probing we re-use the previously setup providers. > > It uses devm to call pci_p2pdma_release() which NULL's pdev->p2pdma. Ah, right. So the /* PCI device was "rebound" to the driver */ comment is further misleading, a new probe would do a new setup. Thanks, Alex
