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

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

[Thorsten Blum]

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 <blum@kernel.org>
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@wunner.de>
---
Changes in v2:
- Add iMac13,x background information and supporting links (Lukas)
- v1: https://lore.kernel.org/r/20260807094601.263450-2-thorsten.blum@linux.dev/
---
 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)

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

[Thorsten Blum]

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@vger.kernel.org
> Signed-off-by: Thorsten Blum <blum@kernel.org>
> 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@wunner.de>
> ---
> Changes in v2:
> - Add iMac13,x background information and supporting links (Lukas)
> - v1: https://lore.kernel.org/r/20260807094601.263450-2-thorsten.blum@linux.dev/
> ---
>  arch/x86/kernel/early-quirks.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)

Gentle ping. Is there anything you'd like to be changed here, or could
someone please pick this up? Thanks.

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

[Dave Hansen]

On 10/3/26 04:49, Thorsten Blum wrote:
> Gentle ping. Is there anything you'd like to be changed here, or could
> someone please pick this up? Thanks.

How has this patch been tested?

One of those links is from 2014.

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

[Thorsten Blum]

On Sat, Oct 03, 2026 at 04:55:54AM -0700, Dave Hansen wrote:
> On 10/3/26 04:49, Thorsten Blum wrote:
> > Gentle ping. Is there anything you'd like to be changed here, or could
> > someone please pick this up? Thanks.
> 
> How has this patch been tested?

I tested it on an iMac13,1, and dmesg confirms the quirk is loaded, but
only when this patch is applied:

[    0.023863] Resetting Apple AirPort card (left enabled by EFI)

lspci also confirms the hole at 00:1c.1.

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

[Thorsten Blum]

On Mon, Oct 05, 2026 at 02:35:47AM +0200, Thorsten Blum wrote:
> On Sat, Oct 03, 2026 at 04:55:54AM -0700, Dave Hansen wrote:
> > On 10/3/26 04:49, Thorsten Blum wrote:
> > > Gentle ping. Is there anything you'd like to be changed here, or could
> > > someone please pick this up? Thanks.
> > 
> > How has this patch been tested?
> 
> I tested it on an iMac13,1, and dmesg confirms the quirk is loaded, but
> only when this patch is applied:
> 
> [    0.023863] Resetting Apple AirPort card (left enabled by EFI)
> 
> lspci also confirms the hole at 00:1c.1.

Hi Dave,

Is there anything else I can do to help get this queued?

Thanks,
Thorsten

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

[Maciej W. Rozycki]

On Mon, 12 Oct 2026, Thorsten Blum wrote:

> Is there anything else I can do to help get this queued?

 FWIW, it's not unusual even if not common for multifunction devices to 
have "holes" in functions, e.g.:

07:00.0 Parallel controller [0701]: Oxford Semiconductor Ltd OXPCIe952 Parallel Port [1415:c118]
07:00.3 Serial controller [0700]: Oxford Semiconductor Ltd OXPCIe952 Native 950 UART [1415:c11b]

which is a chip the functions of which (one or two native or legacy serial 
ports, one parallel port, one GPIO interface) can be activated selectively 
with reset straps, however the resulting numeric 0-3 function assignments 
for individual interfaces are not necessarily contiguous, presumably to 
simplify internal decoding logic.

  Maciej

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

[H. Peter Anvin]

On October 25, 2026 1:07:28 AM PDT, "Maciej W. Rozycki" <macro@orcam.me.uk> wrote:
>On Mon, 12 Oct 2026, Thorsten Blum wrote:
>
>> Is there anything else I can do to help get this queued?
>
> FWIW, it's not unusual even if not common for multifunction devices to 
>have "holes" in functions, e.g.:
>
>07:00.0 Parallel controller [0701]: Oxford Semiconductor Ltd OXPCIe952 Parallel Port [1415:c118]
>07:00.3 Serial controller [0700]: Oxford Semiconductor Ltd OXPCIe952 Native 950 UART [1415:c11b]
>
>which is a chip the functions of which (one or two native or legacy serial 
>ports, one parallel port, one GPIO interface) can be activated selectively 
>with reset straps, however the resulting numeric 0-3 function assignments 
>for individual interfaces are not necessarily contiguous, presumably to 
>simplify internal decoding logic.
>
>  Maciej

Indeed, or there might be multiple versions of a chip with different feature sets – often the same physical chip in different packages, so some features are fused or strapped off because they aren't pinned out.

The assumption that a multifunction service will have all its functions contiguous is absolutely false.

Acked-by: H. Peter Anvin (Rosaic) <hpa@zytor.com>

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@vger.kernel.org
> Signed-off-by: Thorsten Blum <blum@kernel.org>
> 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@wunner.de>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

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@linux.dev/
> ---
>  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)