Re: [PATCH v19 2/2] PCI: Add a quirk for AMD PCIe root ports w/ USB4 controllers

[Lukas Wunner <lukas@wunner.de>]

On Fri, Sep 15, 2023 at 07:04:11AM -0500, Mario Limonciello wrote:
> On 9/15/2023 02:08, Lukas Wunner wrote:
> > On Thu, Sep 14, 2023 at 09:33:54PM -0500, Mario Limonciello wrote:
> > > +static bool child_has_amd_usb4(struct pci_dev *pdev)
> > > +{
> > > +	struct pci_dev *child = NULL;
> > > +
> > > +	while ((child = pci_get_class(PCI_CLASS_SERIAL_USB_USB4, child))) {
> > > +		if (child->vendor != PCI_VENDOR_ID_AMD)
> > > +			continue;
> > > +		if (pcie_find_root_port(child) != pdev)
> > > +			continue;
> > > +		return true;
> > > +	}
> > > +
> > > +	return false;
> > > +}
> > 
> > What's the purpose of the pcie_find_root_port() check?  PCI is a hierarchy,
> > not a graph, so a device cannot have any other Root Port but the one below
> > which you're searching.
> > 
> > If the purpose is to check that the port is a Root Port (if the PCI IDs
> > you're using in the DECLARE_PCI_FIXUP_* clauses match non-Root Ports),
> > check for pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT.  (No need to
> > check for that in every loop iteration obviously, just check once in
> > the fixup.)
> > 
> > Thanks,
> > 
> > Lukas
> 
> The reason to look for it the way that I did was that there are multiple
> root ports with the exact same PCI ID.
> 
> The problem only occurs on the root port that happens to have an AMD USB4
> controller connected.

Yes but what's the purpose of the pcie_find_root_port(child) check
quoted above?

Thanks,

Lukas