Re: [REGRESSION] PCI: Dynamic OF node creation hangs on invalid bridge configuration

[Angel J]

Ok, here it is...

I tested this quirk on Linux 6.18.44 with CONFIG_PCI_DYNAMIC_OF_NODES=y,
and it boots without either OF fix. The diff below omits the test logging.

PCI_FIXUP_HEADER runs after the resources have been parsed using the
original header type, and changing hdr_type also affects configuration
restore. I don't know enough about this part of PCI to judge whether
that's safe, so I'll wait for your advice before submitting it as a patch.

Thanks,
Angel J

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index de9bbccda..57df88a38 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -291,6 +291,22 @@ static int __init pci_apply_final_quirks(void)
 }
 fs_initcall_sync(pci_apply_final_quirks);
 

+/*
+ * On the Dell XPS 8940, 8086:4c43 reports a PCI-to-PCI bridge but has no
+ * downstream bus. Use host-bridge class and a normal header so that
+ * pci_is_bridge() does not send it through bridge scanning.
+ */
+static void quirk_intel_4c43_host_bridge(struct pci_dev *dev)
+{
+	if ((dev->class >> 8) != PCI_CLASS_BRIDGE_PCI ||
+	    dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
+		return;
+
+	dev->class = (PCI_CLASS_BRIDGE_HOST << 8) | (dev->class & 0xff);
+	dev->hdr_type = PCI_HEADER_TYPE_NORMAL;
+}
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x4c43, quirk_intel_4c43_host_bridge);
+
 /*
  * Decoding should be disabled for a PCI device during BAR sizing to avoid
  * conflict. But doing so may cause problems on host bridge and perhaps other

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