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

[PATCH] 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.

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")
Signed-off-by: Thorsten Blum <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] x86/early-quirks: Scan all functions in early_pci_scan_bus()

[Lukas Wunner]

On Fri, Aug 07, 2026 at 11:46:02AM +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.
> 
> 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.

Which device do you need this for?  We should only scan additional
Functions if a quirk needs to applied to them because this extends
boot time.  It requires a justification and shouldn't be done "just
because".

Thanks,

Lukas

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

[Thorsten Blum]

On Sun, Aug 16, 2026 at 07:25:22AM +0200, Lukas Wunner wrote:
> On Fri, Aug 07, 2026 at 11:46:02AM +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.
> > 
> > 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.
> 
> Which device do you need this for?  We should only scan additional
> Functions if a quirk needs to applied to them because this extends
> boot time.  It requires a justification and shouldn't be done "just
> because".

On iMac13,1 and iMac13,2, the BCM4331 AirPort card is behind root port
00:1c.3, also documented by the model list in 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.

[1] https://forum.libreelec.tv/thread/26799-wifi-not-detected-on-2012-imac-in-11-0/
[2] https://zoringroup.com/forum/5/7170/

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

[Lukas Wunner]

On Sun, Aug 16, 2026 at 10:48:17PM +0200, Thorsten Blum wrote:
> On Sun, Aug 16, 2026 at 07:25:22AM +0200, Lukas Wunner wrote:
> > On Fri, Aug 07, 2026 at 11:46:02AM +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.
> > 
> > Which device do you need this for?  We should only scan additional
> > Functions if a quirk needs to applied to them because this extends
> > boot time.  It requires a justification and shouldn't be done "just
> > because".
> 
> On iMac13,1 and iMac13,2, the BCM4331 AirPort card is behind root port
> 00:1c.3, also documented by the model list in 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.
> 
> [1] https://forum.libreelec.tv/thread/26799-wifi-not-detected-on-2012-imac-in-11-0/
> [2] https://zoringroup.com/forum/5/7170/

Thanks for the explanation.  Please include all of this information
in the commit message when respinning.