Re: [PATCH] PCI: Make pcie_find_root_port() work for PCIe root ports as well

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, Jul 01, 2020 at 09:53:51AM +0800, Yicong Yang wrote:
> >  static inline struct pci_dev *pcie_find_root_port(struct pci_dev *dev)
> >  {
> > -	struct pci_dev *bridge = pci_upstream_bridge(dev);
> > -
> > -	while (bridge) {
> > -		if (pci_pcie_type(bridge) == PCI_EXP_TYPE_ROOT_PORT)
> > -			return bridge;
> > -		bridge = pci_upstream_bridge(bridge);
> > +	while (dev) {
> > +		if (pci_is_pcie(dev) &&
> > +		    pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> > +			return dev;
> > +		dev = pci_upstream_bridge(dev);
> >  	}
> >  
> 
> We may have some problems here, as after pcie_find_root_port() called, *dev will
> be either root port or NULL but users may want it unchanged. One such usage is
> in acpi_pci_bridge_d3(), drivers/pci/pci-acpi.c, *dev is used as origin
> after called this.
> 
> So we should use a temporary point to *dev rather than directly modify it.

dev is already a copy of what is passed by the caller so it does not
matter if it gets changed here. You would need to pass it through struct
pci_dev **dev in order to modify the passed pointer.