Re: [PATCH v9 10/18] PCI/P2PDMA: Route Translated Requests under Direct Translated P2P

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Oct 01, 2026 at 02:55:18PM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
> 
> A Downstream Port with ACS Direct Translated P2P enabled routes a Request
> whose Address Type is Translated "to the peer Egress Port without
> redirection, regardless of ACS P2P Request Redirect and ACS P2P Egress
> Control", per PCIe r7.0 sec 6.12.3. P2PDMA assumes every Request carries an
> Untranslated address, so it sends an ATS client through the host bridge
> even where the fabric would route it straight to the peer.

"sends an ATS client through the host bridge" -- I assume this really
means "we told the caller that Requests would be routed through the
host bridge" when in reality they wouldn't?  I don't think this
actually changes any routing in the fabric, does it?

So essentially we told the caller that P2P between A and B was, e.g.,
5 hops when it was really only 2?

> Add PCI_P2PDMA_TLP_TRANSLATED and consult Direct Translated P2P for the
> Requests it describes.
> 
> Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
> Tested-by: Tushar Dave <tdave@nvidia.com>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
>  drivers/pci/p2pdma.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 569a74de3b3a..3fd2cb8d16f0 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -548,6 +548,15 @@ pci_acs_p2pdma_request(u16 ctrl, unsigned int tlp_flags)
>  		 */
>  		if (ctrl & PCI_ACS_TB)
>  			return PCI_ACS_P2PDMA_BLOCKED;
> +
> +		/*
> +		 * PCIe r7.0 sec 6.12.3: ACS Direct Translated P2P routes a
> +		 * Request carrying a Translated address to the peer "without
> +		 * redirection, regardless of ACS P2P Request Redirect and ACS
> +		 * P2P Egress Control settings".
> +		 */
> +		if (ctrl & PCI_ACS_DT)
> +			return PCI_ACS_P2PDMA_DIRECT;
>  	}
>  
>  	return ctrl & (PCI_ACS_RR | PCI_ACS_EC) ?
> 
> -- 
> 2.55.0
>