PCI/ASPM: Don't warn if already in common clock mode

Previously we emitted a warning if we tried to configure common clock mode
the link was already configured to common clock mode by the UEFI BIOS.
Bail out silently in that case instead of emitting the warning:

  pci 0004:00:00.0: ASPM: Could not configure common clock
Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
[bhelgaas: changelog]
Signed-off-by: Bjorn Helgaas <helgaas@kernel.org>

drivers/pci/pcie/aspm.c

@@ -228,6 +228,24 @@ static void pcie_aspm_configure_common_clock(struct pcie_link_state *link)
 	if (!(reg16 & PCI_EXP_LNKSTA_SLC))
 		same_clock = 0;
 
+	/* Port might be already in common clock mode */
+	pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &reg16);
+	if (same_clock && (reg16 & PCI_EXP_LNKCTL_CCC)) {
+		bool consistent = true;
+
+		list_for_each_entry(child, &linkbus->devices, bus_list) {
+			pcie_capability_read_word(child, PCI_EXP_LNKCTL,
+						  &reg16);
+			if (!(reg16 & PCI_EXP_LNKCTL_CCC)) {
+				consistent = false;
+				break;
+			}
+		}
+		if (consistent)
+			return;
+		pci_warn(parent, "ASPM: current common clock configuration is broken, reconfiguring\n");
+	}
+
 	/* Configure downstream component, all functions */
 	list_for_each_entry(child, &linkbus->devices, bus_list) {
 		pcie_capability_read_word(child, PCI_EXP_LNKCTL, &reg16);