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

[Angel J]

Hi Bjorn, Andrea,

Thanks, that clears it up. I agree the of_property fix is simpler. If a
Type 1 device can legitimately have no bus below it, I don't see a reason
to change its class or header just to avoid that case.

The v2 patch is already in the thread. Is there anything you'd like me
to change?

Thanks,
Angel J



On Tuesday, September 15th, 2026 at 18:21, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:

> On Mon, Sep 14, 2026 at 11:28:45PM +0000, Angel J wrote:
> > 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);
> 

> I think your of_property patch is better because it removes some
> assumptions made in the of_pci_make_dev_node() path about what things
> in the pci_dev are valid.  It's quite legal for a device to have a
> Type 1 header (so pci_is_bridge() is true), but have no pci_bus below
> it, e.g., a bridge on bus 0 with Secondary Bus Number also being 0.
> 

> I don't know what happened in this particular case, whether the
> Secondary Bus Number and Subordinate Bus Numbers are hard-wired to
> 0xff or what (per spec, both should be read/write).  Maybe the system
> "lspci -vv" and/or complete dmesg log would have a clue.
> 

> But I do think it's better if we don't assume that every pci_dev with
> a Type 1 header has a pci_bus allocated.
>

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