Re: [REGRESSION] intel-iommu/brcmfmac DMAR fault on Broadcom PCIe wifi, v7.3-rc7 -> v7.3 final -- candidate mechanism and proposed fix path

[Arend van Spriel <arend.vanspriel@broadcom.com>]

Op 20 oktober 2026 18:02:30 schreef Jason Perlow <jperlow@gmail.com>:

> NOTE: an earlier report on this bug from us bounced off one of these lists 
> due to HTML/multipart formatting from the mail client used -- apologies, 
> switching clients. This mail includes the full original report plus a 
> follow-up, merged into one self-contained report since the original never 
> reached anyone.
>
> === ORIGINAL REPORT ===
>
> Hardware: Intel CoffeeLake-H platforms, various. The affected device is a 
> Broadcom BCM4364 802.11ac PCIe wifi adapter (14e4:4464) at 0000:05:00.0 on 
> an Apple MacBookPro16,1 (T2 Mac). Aditya, including you directly since this 
> is T2 hardware; copying iommu/pci/wireless because the fault signature and 
> the fact that it reproduces on only one of five tested machines (at the 
> time of the original report -- see follow-up below, that has since changed) 
> looked like it needed eyes on the core IOMMU/PCI path, not the driver.

[...]

> THE ONE ANOMALY WE CAN'T YET EXPLAIN
>
> Despite the last two items above being unchanged, the actual generated 
> .config has CONFIG_INTEL_IOMMU_DEFAULT_ON unset after make olddefconfig 
> against the rc7 source tree, but =y after the same process against the 
> final source tree, even though our template explicitly answers "# 
> CONFIG_INTEL_IOMMU_DEFAULT_ON is not set" in both cases. Our working theory 
> is that some other symbol started selecting/implying INTEL_IOMMU_DEFAULT_ON 
> between rc7 and final -- which would override an explicitly-seeded "not 
> set" answer during olddefconfig resolution -- but we have not identified 
> which one yet.

Simply run make menuconfig and it should be able to tell you how it is 
selected.

Regards,
Arend>