Public bug reported:
This upstream patch from v7.1 is needed for CXL support. When an
endpoint is below a CXL-mode upstream bridge whose CXL Port Control
"Unmask SBR" bit is clear, Secondary Bus Reset has no hardware effect.
The old probe path still reported success, so sysfs advertised bus in
reset_method even though selecting or falling back to that reset path
would fail. Return -ENOTTY during probe for masked CXL SBR so bus is not
advertised when the platform cannot perform it.
Patch: 702c1d5 PCI/CXL: Hide SBR from reset_methods if masked by CXL
Testing
Built and booted patched 6.17 kernel on vr-nvl72-ts1-l10-comp016:
Linux vr-nvl72-ts1-l10-comp016 7.0.0hide_sbr_cxl_70-bos+ #2 SMP
PREEMPT_DYNAMIC Tue May 26 15:02:51 UTC 2026 aarch64 aarch64 aarch64
GNU/Linux
Validated PCI/CXL reset-method behavior with a scanner that checks each
endpoint's immediate upstream bridge for:
- CXL Port DVSEC present
- CXL Flex Bus DVSEC status indicating CXL mode
- CXL Port Control Unmask SBR clear
- endpoint reset_method does not advertise bus
Results:
0002:81:00.0 sbr masked cxl yes has_bus no PASS_BUS_HIDDEN
0002:c1:00.0 sbr masked cxl yes has_bus no PASS_BUS_HIDDEN
000a:81:00.0 sbr masked cxl yes has_bus no PASS_BUS_HIDDEN
000a:e1:00.0 sbr masked cxl yes has_bus no PASS_BUS_HIDDEN
summary: cxl_related=28 masked_cxl_targets=4 failures=0
Non-CXL-mode bridges continued to report NOT_CXL_MODE, so the behavior
remains scoped to CXL-mode upstream bridges with SBR masked.
** Affects: linux-nvidia-6.17 (Ubuntu)
Importance: Undecided
Status: New
** Affects: linux-nvidia-bos (Ubuntu)
Importance: Undecided
Status: New
** Also affects: linux-nvidia-bos (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2154302
Title:
Backport PCI/CXL: Hide SBR from reset_methods if masked by CXL
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