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

[nirmoy]

Summary

• Add a PCI final/early-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 during early 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

• Current PR head: b8a7745cab1c3c7be7b25c2dbba0f038662b60f6.
• 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-pr447-quirks-build -j$(nproc) drivers/pci/quirks.o
• Built arm64 packages on the GB200 build host with make bindeb-pkg after removing the 64-bit upstream BAR0 skip.
• Installed and booted the Quark DUT: OS 172.17.33.143 via jumper 10.22.18.250; BMC 172.17.33.144.

Linux localhost-right 6.18.33-pr447-pericom-no64 #1 SMP PREEMPT_DYNAMIC Fri May 29 19:03:57 UTC 2026 aarch64

• 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

• Rootfs stayed read-write on the NVMe/BTRFS device:

/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

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

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|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.
• The 24.04 DUT has an unrelated DKMS failure for mods/4.31.0 on test kernels, so 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
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: b8a7745cab1c

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