linux-kernel - Re: [PATCH] Whitelist AMD host bridge device(s) to enable P2P DMA

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Date:   Wed, 11 Aug 2021 15:29:03 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Ramesh Errabolu <Ramesh.Errabolu@....com>
Cc:     amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Whitelist AMD host bridge device(s) to enable P2P DMA

On Wed, Aug 11, 2021 at 3:11 PM Ramesh Errabolu <Ramesh.Errabolu@....com> wrote:
>
> Current implementation will disallow P2P DMA if the participating
> devices belong to different root complexes. Implementation allows
> this default behavior to be overridden for whitelisted devices. The
> patch adds an AMD host bridge to be whitelisted

Why do we need this?  cpu_supports_p2pdma() should return true for all
AMD Zen CPUs.

Alex

>
> Signed-off-by: Ramesh Errabolu <Ramesh.Errabolu@....com>
> ---
>  drivers/pci/p2pdma.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 196382630363..7003bb9faf23 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -305,6 +305,8 @@ static const struct pci_p2pdma_whitelist_entry {
>         {PCI_VENDOR_ID_INTEL,   0x2032, 0},
>         {PCI_VENDOR_ID_INTEL,   0x2033, 0},
>         {PCI_VENDOR_ID_INTEL,   0x2020, 0},
> +       /* AMD Host Bridge Devices */
> +       {PCI_VENDOR_ID_AMD,     0x1480, 0},
>         {}
>  };
>
> --
> 2.31.1
>