Kernel: support second VMD rootbus on Arrow Lake (fixes #107)#113
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Kernel: support second VMD rootbus on Arrow Lake (fixes #107)#113mastacontrola wants to merge 1 commit into
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On Arrow Lake desktop (Core Ultra 200S) systems with VMD enabled, NVMe drives routed through the PCH live on a second VMD rootbus hardwired to bus 0x80. The mainline vmd driver only enumerates the first rootbus, so FOS never sees the disk and imaging fails. Intel's upstream fix (v5, 2026-06-25) is not yet merged in any mainline/stable kernel, so a kernel version bump cannot fix this yet. Ubuntu ships the same fix as SAUCE patches in linux-oem-6.11 (Launchpad #2085853), where it is confirmed working on affected hardware. This adds those four patches (0c9ff92b2efc, d20355bdd463, e7b7195e3706, 040d304c75b9) combined and adapted to vanilla 6.12.35 as patch/kernel/linux.patch, which build.sh already applies to all kernel builds. The patched vmd.c was diffed against Ubuntu's final tree to confirm only known base-version differences remain, and the patch was verified to apply cleanly the same way build.sh does. Harmless for arm64/x86 builds: the file patches identically and CONFIG_VMD is only enabled on x64. Fixes #107 Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Problem
On Arrow Lake desktop platforms (Core Ultra 200S) with VMD enabled in BIOS, NVMe drives attached through the PCH sit on a second VMD rootbus hardwired to bus
0x80. The mainlinevmddriver only enumerates the first rootbus, so the drive is invisible to FOS — imaging fails with no disks found (#107). Arrow Lake laptops (H/HX/U) route NVMe over CPU lanes on the first rootbus, which is why they work fine today.Why not just bump the kernel
Intel's upstream fix ("PCI: vmd: Add support for second rootbus under VMD", Szymon Durawa) is at v5 (2026-06-25) and still unmerged — no mainline or stable kernel has it, so no version bump can fix this yet.
What this does
Ubuntu ships the fix as SAUCE patches in
linux-oem-6.11(Launchpad #2085853), confirmed working on affected hardware since 6.11.0-1008.8. This PR combines those four commits and adapts them to our vanilla 6.12.35 aspatch/kernel/linux.patch, whichbuild.shalready picks up automatically for all kernel builds:0c9ff92b2efcUBUNTU: SAUCE: PCI: vmd: Clean up vmd_enable_domain functiond20355bdd463UBUNTU: SAUCE: PCI: vmd: Add VMD PCH rootbus supporte7b7195e3706UBUNTU: SAUCE: PCI: vmd: Add WA for VMD PCH rootbus support040d304c75b9UBUNTU: SAUCE: PCI: vmd: Fix use-after-free bug in resource name assignmentAdaptation to 6.12.35: dropped the
pci_lock_rescan_remove()/pci_unlock_rescan_remove()calls and theaspm_os_controlfield, which exist only in Ubuntu's tree. Everything else is verbatim.Verification
vmd.cwas diffed against Ubuntu's final tree at040d304c75b9: the only remaining differences are known 6.11↔6.12.35 base deltas (raw spinlocks, Xen bypass block,MSI_FLAG_NO_AFFINITY) plus the two Ubuntu-only items above.patch -p1against a pristine 6.12.35 tree — the exact invocationbuild.shuses — and reproduces the validated file byte-for-byte.drivers/pci/controller/vmd.obuilds cleanly (zero warnings atW=1) against vanilla 6.12.35 configured withconfigs/kernelx64.config(CONFIG_VMD=y).The patch file carries a provenance header noting it should be removed once the upstream series lands in whatever stable kernel FOS builds from.
Fixes #107
🤖 Generated with Claude Code