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

[Thorsten Blum <thorsten.blum@linux.dev>]

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>
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]
---
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)