On Tue, Sep 23, 2025 at 12:09:32PM -0600, Alex Williamson wrote:
On Tue, 23 Sep 2025 14:43:33 -0300 Jason Gunthorpe jgg@nvidia.com 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@nvidia.com 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.
I'll change it now. If "enable" function goes to be "get" function, we won't need to store anything in vfio_pci_dma_buf too. At the end, we have exactly two lines "provider = priv->vdev->provider[priv->bar];", which can easily be changed to be "provider = pcim_p2pdma_provider(priv->vdev->pdev, priv->bar)"
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,
I will fix the comment.
Thanks
Alex