[linux-nvidia-6.18-next] PCI: mirror PI7C9X3G606GPC Port 4 BAR0

[nirmoy]

Summary

• Add a PCI final/resume quirk for the Diodes/Pericom PI7C9X3G606GPC switch.
• Mirror the immediate upstream port BAR0 value into downstream Port 4 BAR0 after Linux PCI resource assignment and after resume.
• Scope the WAR to the Diodes-confirmed OS-visible Tile0/P4 mapping: upstream bus + 1, device 04, function 0.
• Port 4 BAR0 can read back as zero through normal PCI config space even after a successful write, so the quirk rewrites BAR0 whenever it runs.

Validation

• Local patch checks at head 8654dc24d9b6bcad10b527cb9c11e64c7aab48c9 passed:
  • scripts/checkpatch.pl --strict --ignore GERRIT_CHANGE_ID --git HEAD
  • git diff --check HEAD~1..HEAD
• Built arm64 packages on the GB200 build host with make bindeb-pkg and installed image/headers on the Quark DUT.
• The current PR head 8654dc24d9b6bcad10b527cb9c11e64c7aab48c9 is a message-only respin from the tested package commit 7f1b4f6fd0544b30133c956da5022f49c8fe8b71; git diff 7f1b4f6fd0544b30133c956da5022f49c8fe8b71..8654dc24d9b6bcad10b527cb9c11e64c7aab48c9 --stat is empty.
• Booted the DUT on the PR kernel:

Linux localhost-right 6.18.33-pr447-pericom+ #pr447 SMP PREEMPT_DYNAMIC Thu May 28 20:46:09 UTC 2026 aarch64
/dev/nvme0n1p2[/@root/versions/v-diagos-snapshot-20260421] btrfs rw,relatime,ssd,discard=async,space_cache=v2,subvolid=264,subvol=/@root/versions/v-diagos-snapshot-20260421

• Confirmed the affected topology and quirk application from the boot journal:

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

• Ran a 300 second NVMe-backed rootfs fio smoke test:

pr447-rootfs-smoke: err= 0
READ: bw=251MiB/s, io=73.6GiB, run=300001msec
WRITE: bw=108MiB/s, io=31.6GiB, run=300001msec

• Post-fio journalctl -b -k scan for BTRFS error|I/O error|nvme.*timeout|device inaccessible|read-only|blk_update_request|Buffer I/O error returned no matches.
• Did not use the Diodes BMC/I2C BAR0 readback helper in this validation run. That helper uses special CPED/CDEP programming and is not a supported production validation path on this platform.

References

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

6.17 PR: #442
BOS PR: #443
NVBug: https://nvbugspro.nvidia.com/bug/6205517
NVBug: https://nvbugspro.nvidia.com/bug/6134331

[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: 8654dc24d9b6

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