Re: [PATCH v2] x86/early-quirks: Scan all functions in early_pci_scan_bus()

[Lukas Wunner <lukas@wunner.de>]

On Mon, Aug 17, 2026 at 11:00:13AM +0200, Thorsten Blum wrote:
> early_pci_scan_bus() stops scanning a PCI slot when check_dev_quirk()
> returns nonzero, which avoids probing functions 1-7 on single-function
> devices, but also stops scanning when a function is absent on a
> multifunction device.
> 
> This can skip early quirks on multifunction devices with holes in their
> function numbering.
> 
> On iMac13,1 and iMac13,2, the BCM4331 AirPort card is behind root port
> 00:1c.3, also documented by the model list in commit abb2bafd295f
> ("x86/quirks: Add early quirk to reset Apple AirPort card").
> 
> Public lspci output for 2012 iMacs [1][2] shows that 00:1c.0, 00:1c.2,
> 00:1c.3 and 00:1c.4 are present, but 00:1c.1 is missing. The old code
> stops at 00:1c.1 and never reaches 00:1c.3, so the AirPort reset quirk
> is silently skipped on these machines.
> 
> Check function 0 first, and if it indicates a multifunction device, scan
> functions 1-7 independently so that absent functions do not cause later
> ones to be skipped.
> 
> Fixes: 15650a2f644a ("x86/PCI: fixup early quirk probing")
> Cc: stable@vger.kernel.org
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>

Reviewed-by: Lukas Wunner <lukas@wunner.de>

I'm wondering if the Fixes tag should rather refer to abb2bafd295f
("x86/quirks: Add early quirk to reset Apple AirPort card"),
or whether it's necessary at all given the relatively small number
of affected machines.

This will slightly lengthen boot time as all 8 functions of
multifunction devices are probed, but that is mitigated by the
existing check for an "all ones" response to the config space read
of PCI_CLASS_DEVICE:  The remainder of check_dev_quirk() is skipped
for non-responsive Functions.

Thanks,

Lukas