On Sun, Oct 20, 2024 at 10:21:29PM -0700, Vivek Kasireddy wrote:
> Functions of the same PCI device (such as a PF and a VF) share the
> same bus and have a common root port and typically, the PF provisions
> resources for the VF. Therefore, they can be considered compatible
> as far as P2P access is considered.
>
> Currently, although the distance (2) is correctly calculated for
> functions of the same device, an ACS check failure prevents P2P DMA
> access between them. Therefore, introduce a small function named
> pci_devs_are_p2pdma_compatible() to determine if the provider and
> client belong to the same device and facilitate P2P DMA between
> them by not enforcing the ACS check.
>
> v2:
> - Relax the enforcment of ACS check only for Intel GPU functions
> as they are P2PDMA compatible given the way the PF provisions
> the resources among multiple VFs.
I don't want version history in the commit log. If the content is
useful, just incorporate it here directly (without the version info),
and put the version-to-version changelog below the "---".
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> Cc: <linux-pci@xxxxxxxxxxxxxxx>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
> ---
> drivers/pci/p2pdma.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 4f47a13cb500..a230e661f939 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -535,6 +535,17 @@ static unsigned long map_types_idx(struct pci_dev *client)
> return (pci_domain_nr(client->bus) << 16) | pci_dev_id(client);
> }
>
> +static bool pci_devs_are_p2pdma_compatible(struct pci_dev *provider,
> + struct pci_dev *client)
> +{
> + if (provider->vendor == PCI_VENDOR_ID_INTEL) {
> + if (pci_is_vga(provider) && pci_is_vga(client))
> + return pci_physfn(provider) == pci_physfn(client);
> + }
This doesn't explain why this should be specific to Intel or VGA. As
far as I can tell, everything mentioned in the commit log is generic.
I see the previous comments
(https://lore.kernel.org/all/eddb423c-945f-40c9-b904-43ea8371f1c4@xxxxxxxxxxxx/),
but none of that context was captured here.
I'm not sure what you refer to by "PF provisions resources for the
VF". Isn't it *always* the case that the architected PCI resources
(BARs) are configured by the PF? It sounds like you're referring to
something Intel GPU-specific beyond that?
> + return false;
> +}
> +
> /*
> * Calculate the P2PDMA mapping type and distance between two PCI devices.
> *
> @@ -634,7 +645,7 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
>
> *dist = dist_a + dist_b;
>
> - if (!acs_cnt) {
> + if (!acs_cnt || pci_devs_are_p2pdma_compatible(provider, client)) {
> map_type = PCI_P2PDMA_MAP_BUS_ADDR;
> goto done;
> }
> @@ -696,7 +707,9 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
> return -1;
>
> for (i = 0; i < num_clients; i++) {
> - pci_client = find_parent_pci_dev(clients[i]);
> + pci_client = dev_is_pf(clients[i]) ?
> + pci_dev_get(to_pci_dev(clients[i])) :
> + find_parent_pci_dev(clients[i]);
> if (!pci_client) {
> if (verbose)
> dev_warn(clients[i],
> --
> 2.45.1
>
