On Tue, Oct 06, 2026 at 05:21:09PM -0500, Bjorn Helgaas wrote:
On Thu, Oct 01, 2026 at 02:55:16PM +0300, Leon Romanovsky wrote:
From: Leon Romanovsky leonro@nvidia.com
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.
The mlx5 patch, which is currently on hold, uses the PCI_P2PDMA_TLP_RELAXED_CPL TLP flag to dynamically enable or disable ATS.
https://lore.kernel.org/all/20260920-fix-p2p-acs-v4-0-v7-19-ca0828ab697c@nvi...
Thanks
Add enum pci_p2pdma_tlp_flags and let a caller state that property.
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 | 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