PCI: Access Link 2 registers only for devices with Links

PCIe r2.0, sec 7.8 added Link Capabilities/Status/Control 2 registers to
the PCIe Capability with Capability Version 2.

Previously we assumed these registers were implemented for all PCIe
Capabilities of version 2 or greater, but in fact they are only
implemented for devices with Links.

Update pcie_capability_reg_implemented() to check whether the device has
a Link.

[bhelgaas: commit log, squash export]
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2209100057070.2275@angie.orcam.me.uk
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2209100057300.2275@angie.orcam.me.uk
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/access.c

@@ -350,6 +350,11 @@ bool pcie_cap_has_lnkctl(const struct pci_dev *dev)
 	       type == PCI_EXP_TYPE_PCIE_BRIDGE;
 }
 
+bool pcie_cap_has_lnkctl2(const struct pci_dev *dev)
+{
+	return pcie_cap_has_lnkctl(dev) && pcie_cap_version(dev) > 1;
+}
+
 static inline bool pcie_cap_has_sltctl(const struct pci_dev *dev)
 {
 	return pcie_downstream_port(dev) &&
@@ -390,10 +395,11 @@ static bool pcie_capability_reg_implemented(struct pci_dev *dev, int pos)
 		return pcie_cap_has_rtctl(dev);
 	case PCI_EXP_DEVCAP2:
 	case PCI_EXP_DEVCTL2:
+		return pcie_cap_version(dev) > 1;
 	case PCI_EXP_LNKCAP2:
 	case PCI_EXP_LNKCTL2:
 	case PCI_EXP_LNKSTA2:
-		return pcie_cap_version(dev) > 1;
+		return pcie_cap_has_lnkctl2(dev);
 	default:
 		return false;
 	}

drivers/pci/pci.h

@@ -15,6 +15,7 @@ extern const unsigned char pcie_link_speed[];
 extern bool pci_early_dump;
 
 bool pcie_cap_has_lnkctl(const struct pci_dev *dev);
+bool pcie_cap_has_lnkctl2(const struct pci_dev *dev);
 bool pcie_cap_has_rtctl(const struct pci_dev *dev);
 
 /* Functions internal to the PCI core code */