[PATCH v6 0/2] PCI: AtomicOps: Fix pci_enable_atomic_ops_to_root()

Gerd Bayer
2026-03-25T15:16:34Z

Hi Bjorn et al.

On s390, AtomicOp Requests are enabled on a PCI function that supports
them, despite the helper being ignorant about the root port's capability
to supporting their completion.

Patch 1: Fix the logic in pci_enable_atomic_ops_to_root()
Patch 2: Update references to PCIe spec in that function.

I did test that the issue is fixed with these patches. Also, I verified
that on a Mellanox/Nvidia ConnectX-6 adapter plugged straight into the
root port of a x86 system still gets AtomicOp Requests enabled.

Due to lacking the required hardware, I did not test this with any PCIe
switches between root port and endpoint. So test exposure to other
environments is highly appreciated. One particularly rare setup is a
RCiEP that might act as a AtomicOps Requestor - but was subject to a
regression in v4 as reported by Sashiko.

v5 of this series tries to make no functional changes for that class of
devices either.

Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
---
Changes in v6:
- Incorporate Ilpo's editorial comments.
- Correct logic in pci_is_atomicops_capable_rp() (annotated by Sashiko)
- Link to v5: https://lore.kernel.org/r/20260323-fix_pciatops-v5-0-fada7233aea8@linux.ibm.com

Changes in v5:
- Introduce new pcibios_connects_to_atomicops_capable_rc() so arch's can
declare AtomicOps support outside of PCIe config space. Defaults to
"true" - except s390.
- rebase to 7.0-rc5
- Link to v4: https://lore.kernel.org/r/20260313-fix_pciatops-v4-0-93bc70a63935@linux.ibm.com

Changes in v4:
- drop patch 1 - it will become the base of a new series
- previous patch 2, now 1: reword commit message
- add a new patch to update references to PCI spec within
pci_enable_atomic_ops_to_root()
- rebase to latest master
- Link to v3: https://lore.kernel.org/r/20260306-fix_pciatops-v3-0-99d12bcafb19@linux.ibm.com

Changes in v3:
- rebase to 7.0-rc2
- gentle ping
- add netdev and rdma lists for awareness
- Link to v2: https://lore.kernel.org/r/20251216-fix_pciatops-v2-0-d013e9b7e2ee@linux.ibm.com

Changes in v2:
- rebase to 6.19-rc1
- otherwise unchanged to v1
- Link to v1: https://lore.kernel.org/r/20251110-fix_pciatops-v1-0-edc58a57b62e@linux.ibm.com

---
Gerd Bayer (2):
PCI: AtomicOps: Do not enable without support in root complex
PCI: AtomicOps: Update references to PCIe spec

arch/s390/pci/pci.c | 5 +++++
drivers/pci/pci.c | 54 +++++++++++++++++++++++++++++++++--------------------
include/linux/pci.h | 1 +
3 files changed, 40 insertions(+), 20 deletions(-)
---
base-commit: c369299895a591d96745d6492d4888259b004a9e
change-id: 20251106-fix_pciatops-7e8608eccb03

Best regards,
--
Gerd Bayer <gbayer@linux.ibm.com>