[26.04_linux-nvidia-bos] PCI: mirror PI7C9X3G606GPC Port 4 BAR0

[nirmoy]

Summary

• Backport the PI7C9X3G606GPC Port 4 BAR0 workaround from the 6.17 PR.
• Add a PCI final/early-resume quirk to mirror the upstream BAR0 value into downstream Port 4 BAR0.
• Scope the WAR to the Diodes-confirmed OS-visible Tile0/P4 mapping: upstream bus + 1, device 04, function 0.
• Port 4 BAR0 may read back as zero through normal PCI config space even after a successful write, so the quirk rewrites BAR0 whenever it runs.

Validation

• Current PR head: a69e886f8becb7608a3ca2e26315d384383c82ab.
• Local patch checks passed at current head:
  • scripts/checkpatch.pl --strict --ignore GERRIT_CHANGE_ID --git HEAD
  • git diff --check HEAD~1..HEAD
  • make O=/tmp/nv-kernels-pr443-quirks-build -j$(nproc) drivers/pci/quirks.o
• Previous BOS package validation booted 7.0.0-2007-nvidia-bos-64k on the Quark DUT: OS 172.17.33.143 via jumper 10.22.18.250; BMC 172.17.33.144.

Linux localhost-right 7.0.0-2007-nvidia-bos-64k #7 SMP PREEMPT_DYNAMIC Thu May 28 19:54:58 UTC 2026 aarch64

• Quirk/topology evidence from the booted BOS kernel:

pci 0002:a1:00.0: BAR 0 [mem 0x10300000-0x1037ffff]
pci 0002:a2:04.0: [12d8:c008] type 01 class 0x060400 PCIe Switch Downstream Port
pci 0002:a3:00.0: [1344:51c3] type 00 class 0x010802 PCIe Endpoint
pci 0002:a1:00.0: BAR 0 [mem 0x10300000-0x1037ffff]: assigned
pci 0002:a2:04.0: wrote upstream BAR 0 0x10300000 to Port 4 BAR 0 for PI7C9X3G606GPC BAR0 mirror workaround

• Retested the equivalent 6.18 PR code after removing the 64-bit upstream BAR0 skip. The Quark DUT booted 6.18.33-pr447-pericom-no64 and showed the quirk still firing:

pci 0002:a1:00.0: BAR 0 [mem 0x10300000-0x1037ffff]: assigned
pci 0002:a2:04.0: wrote upstream BAR 0 0x10300000 to Port 4 BAR 0 for PI7C9X3G606GPC BAR0 mirror workaround

• Ran a 300s fio randrw smoke on the NVMe-backed rootfs with the no-64-skip test kernel:

pr447-no64-rootfs-smoke: err= 0
READ: bw=251MiB/s, io=73.6GiB, run=300009msec
WRITE: bw=108MiB/s, io=31.6GiB, run=300009msec

• Post-fio journalctl -b -k scan for BTRFS error, I/O error, nvme.*timeout, device inaccessible, read-only, blk_update_request, and Buffer I/O error returned no matches.
• Did not use the BMC/I2C BAR0 readback helper for this validation. The Quark platform owner said that helper uses special CPED/CDEP access that is not supported as routine validation on this platform and can put the PCIe switch into a bad state.

Notes:

• The 24.04 DUT needed a temporary run-parts compatibility wrapper to run the 26.04 BOS kernel maintscripts, which pass multiple hook directories. The wrapper was removed after package configuration.
• OFED/DKMS modules on this 24.04 DUT report unsupported test-kernel headers for some test kernels. DKMS hooks were temporarily bypassed only to finish package configuration/initramfs/grub; hooks were restored afterward.

References

Launchpad: https://bugs.launchpad.net/ubuntu/+source/linux-nvidia-6.17/+bug/2154457

6.17 PR: #442
NVBug: https://nvbugspro.nvidia.com/bug/6205517
NVBug: https://nvbugspro.nvidia.com/bug/6134331

[github-actions]

PR Validation Report

Patchscan ✅ No Missing Fixes

All cherry-picked commits checked — no missing upstream fixes found.

PR Lint ✅ All checks passed

Details

Checking 1 commits...

Cherry-pick digest:
┌──────────────┬──────────────────────────────────────────────────────────────────┬────────────┬─────────┬───────────────────────────┐
│ Local        │ Referenced upstream / Patch subject                              │ Patch-ID   │ Subject │ SoB chain                 │
├──────────────┼──────────────────────────────────────────────────────────────────┼────────────┼─────────┼───────────────────────────┤
│ a69e886f8bec │ [SAUCE] pci: quirks: mirror pi7c9x3g606gpc port 4 bar0           │ N/A        │ N/A     │ nirmoyd                   │
└──────────────┴──────────────────────────────────────────────────────────────────┴────────────┴─────────┴───────────────────────────┘

Lint: all checks passed.

[nirmoy]

Boro review

Summary

No issues found across the reviewed commits.

Findings: no problems found

Latest watcher review: open review

Kernel deb build: successful (download debs, 4 files)

Head: a69e886f8bec

This comment is maintained by nv-pr-bot. It is updated when the GitHub watcher publishes a newer review.