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

[Gerd Bayer]

Hi Bjorn et al.

this series addresses a few issues that have come up with the helper
function that enables Atomic Op Requests to be initiated by PCI
enpoints:

A. Most in-tree users of this helper use it incorrectly [0].
B. On s390, Atomic Op Requests are enabled, although the helper
   cannot know whether the root port is really supporting them.
C. Loop control in the helper function does not guarantee that a root
   port's capabilities are ever checked against those requested by the
   caller.

Address these issue with the following patches:
Patch 1: Make it harder to mis-use the enablement function,
Patch 2: Addresses issues B. and C.

I did test that issue B is fixed with these patches. Also, I verified
that Atomic Ops enablement on a Mellanox/Nvidia ConnectX-6 adapter
plugged straight into the root port of a x86 system still gets AtomicOp
Requests enabled. However, I did not test this with any PCIe switches
between root port and endpoint.

Ideally, both patches would be incorporated immediately, so we could
start correcting the mis-uses in the device drivers. I don't know of any
complaints when using Atomic Ops on devices where the driver is
mis-using the helper. Patch 2 however, is fixing an obseved issue.

[0]: https://lore.kernel.org/all/fbe34de16f5c0bf25a16f9819a57fdd81e5bb08c.camel@xxxxxxxxxxxxx/
[1]: https://lore.kernel.org/all/20251105-mlxatomics-v1-0-10c71649e08d@xxxxxxxxxxxxx/

Signed-off-by: Gerd Bayer <gbayer@xxxxxxxxxxxxx>
---
Gerd Bayer (2):
      PCI: AtomicOps: Define valid root port capabilities
      PCI: AtomicOps: Fix logic in enable function

 drivers/pci/pci.c             | 43 +++++++++++++++++++++----------------------
 include/uapi/linux/pci_regs.h |  8 ++++++++
 2 files changed, 29 insertions(+), 22 deletions(-)
---
base-commit: e9a6fb0bcdd7609be6969112f3fbfcce3b1d4a7c
change-id: 20251106-fix_pciatops-7e8608eccb03

Best regards,
-- 
Gerd Bayer <gbayer@xxxxxxxxxxxxx>