Re: [PATCH v9 08/18] PCI/P2PDMA: Route Relaxed Ordering Completions directly

[Bjorn Helgaas]

On Thu, Oct 01, 2026 at 02:55:16PM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@xxxxxxxxxx>
> 
> ACS P2P Completion Redirect leaves Completions carrying the Relaxed
> Ordering attribute alone. PCIe r7.0 sec 6.12.1.1 redirects only those "that
> do not have the Relaxed Ordering Attribute bit set", and sec 7.7.12.5
> describes the enable bit as "applicable only to Completions whose Relaxed
> Ordering Attribute is clear". P2PDMA reports one answer for every kind of
> TLP, so a client whose provider returns such Completions is sent through
> the host bridge for a redirect that never happens to it.

I guess pci_acs_p2pdma_completion() returned PCI_ACS_P2PDMA_REDIRECT
even for RO Completions?  But that didn't change the hardware
behavior -- maybe the caller *thought* Completions were routed through
the host bridge, but they actually weren't.

I kind of lost the plot here.  What does the caller do with this
information?  I don't think a device is *required* to set RO even when
it is enabled, and it may set RO on some transactions but not others.

> Add enum pci_p2pdma_tlp_flags and let a caller state that property.
> 
> Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> Tested-by: Tushar Dave <tdave@xxxxxxxxxx>
> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
> ---
>  drivers/pci/p2pdma.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 43e225cc5735..1fadef6d0609 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -544,11 +544,15 @@ pci_acs_p2pdma_request(u16 ctrl, unsigned int tlp_flags)
>  /*
>   * Decide how a peer-to-peer Completion at an ACS-capable ingress port routes.
>   * PCIe r7.0 sec 6.12.1.1: no ACS control other than P2P Completion Redirect
> - * affects a Completion.
> + * affects a Completion, and that one leaves Completions carrying the Relaxed
> + * Ordering attribute alone.
>   */
>  static enum pci_acs_p2pdma_state
>  pci_acs_p2pdma_completion(u16 ctrl, unsigned int tlp_flags)
>  {
> +	if (tlp_flags & PCI_P2PDMA_TLP_RELAXED_CPL)
> +		return PCI_ACS_P2PDMA_DIRECT;
> +
>  	return ctrl & PCI_ACS_CR ? PCI_ACS_P2PDMA_REDIRECT :
>  				   PCI_ACS_P2PDMA_DIRECT;
>  }
> 
> -- 
> 2.55.0
>