Re: [RFC PATCH 1/5] pci/p2p: add a function to test peer to peer capability

[Alex Deucher <alexdeucher@gmail.com>]

On Tue, Jan 29, 2019 at 12:47 PM <jglisse@redhat.com> wrote:
>
> From: Jérôme Glisse <jglisse@redhat.com>
>
> device_test_p2p() return true if two devices can peer to peer to
> each other. We add a generic function as different inter-connect
> can support peer to peer and we want to genericaly test this no
> matter what the inter-connect might be. However this version only
> support PCIE for now.
>

What about something like these patches:
https://cgit.freedesktop.org/~deathsimple/linux/commit/?h=p2p&id=4fab9ff69cb968183f717551441b475fabce6c1c
https://cgit.freedesktop.org/~deathsimple/linux/commit/?h=p2p&id=f90b12d41c277335d08c9dab62433f27c0fadbe5
They are a bit more thorough.

Alex

> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Rafael J. Wysocki <rafael@kernel.org>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Christian Koenig <christian.koenig@amd.com>
> Cc: Felix Kuehling <Felix.Kuehling@amd.com>
> Cc: Jason Gunthorpe <jgg@mellanox.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pci@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: iommu@lists.linux-foundation.org
> ---
>  drivers/pci/p2pdma.c       | 27 +++++++++++++++++++++++++++
>  include/linux/pci-p2pdma.h |  6 ++++++
>  2 files changed, 33 insertions(+)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index c52298d76e64..620ac60babb5 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -797,3 +797,30 @@ ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
>         return sprintf(page, "%s\n", pci_name(p2p_dev));
>  }
>  EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);
> +
> +bool pci_test_p2p(struct device *devA, struct device *devB)
> +{
> +       struct pci_dev *pciA, *pciB;
> +       bool ret;
> +       int tmp;
> +
> +       /*
> +        * For now we only support PCIE peer to peer but other inter-connect
> +        * can be added.
> +        */
> +       pciA = find_parent_pci_dev(devA);
> +       pciB = find_parent_pci_dev(devB);
> +       if (pciA == NULL || pciB == NULL) {
> +               ret = false;
> +               goto out;
> +       }
> +
> +       tmp = upstream_bridge_distance(pciA, pciB, NULL);
> +       ret = tmp < 0 ? false : true;
> +
> +out:
> +       pci_dev_put(pciB);
> +       pci_dev_put(pciA);
> +       return false;
> +}
> +EXPORT_SYMBOL_GPL(pci_test_p2p);
> diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
> index bca9bc3e5be7..7671cc499a08 100644
> --- a/include/linux/pci-p2pdma.h
> +++ b/include/linux/pci-p2pdma.h
> @@ -36,6 +36,7 @@ int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
>                             bool *use_p2pdma);
>  ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
>                                bool use_p2pdma);
> +bool pci_test_p2p(struct device *devA, struct device *devB);
>  #else /* CONFIG_PCI_P2PDMA */
>  static inline int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar,
>                 size_t size, u64 offset)
> @@ -97,6 +98,11 @@ static inline ssize_t pci_p2pdma_enable_show(char *page,
>  {
>         return sprintf(page, "none\n");
>  }
> +
> +static inline bool pci_test_p2p(struct device *devA, struct device *devB)
> +{
> +       return false;
> +}
>  #endif /* CONFIG_PCI_P2PDMA */
>
>
> --
> 2.17.2
>
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