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

[Bjorn Helgaas]

On Wed, Sep 16, 2026 at 12:02:07PM +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@xxxxxxxxxxxxxxx
> Signed-off-by: Thorsten Blum <blum@xxxxxxxxxx>
> Link: https://forum.libreelec.tv/thread/26799-wifi-not-detected-on-2012-imac-in-11-0/ [1]
> Link: https://zoringroup.com/forum/5/7170/ [2]
> Reviewed-by: Lukas Wunner <lukas@xxxxxxxxx>

Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

Let me know if you'd prefer this to be merged via the PCI tree.

> ---
> Changes in v2:
> - Add iMac13,x background information and supporting links (Lukas)
> - v1: https://lore.kernel.org/r/20260807094601.263450-2-thorsten.blum@xxxxxxxxx/
> ---
>  arch/x86/kernel/early-quirks.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
> index 6b6f32f40cbe..c641f38eca3a 100644
> --- a/arch/x86/kernel/early-quirks.c
> +++ b/arch/x86/kernel/early-quirks.c
> @@ -795,12 +795,14 @@ static void __init early_pci_scan_bus(int bus)
>  	int slot, func;
>  
>  	/* Poor man's PCI discovery */
> -	for (slot = 0; slot < 32; slot++)
> -		for (func = 0; func < 8; func++) {
> -			/* Only probe function 0 on single fn devices */
> -			if (check_dev_quirk(bus, slot, func))
> -				break;
> -		}
> +	for (slot = 0; slot < 32; slot++) {
> +		/* Only multifunction devices may have functions 1-7 */
> +		if (check_dev_quirk(bus, slot, 0))
> +			continue;
> +
> +		for (func = 1; func < 8; func++)
> +			check_dev_quirk(bus, slot, func);
> +	}
>  }
>  
>  void __init early_quirks(void)