PCI: pciehp: Do not clear Presence Detect Changed during initialization

It is possible that the hotplug event has already happened before the
driver is attached to a PCIe hotplug downstream port. If we just clear the
status we never get the hotplug interrupt and thus the event will be
missed.

To make sure that does not happen, we leave Presence Detect Changed bit
untouched during initialization. Then once the event is unmasked we get an
interrupt and handle the hotplug event properly.
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

drivers/pci/hotplug/pciehp_hpc.c

@@ -858,11 +858,16 @@ struct controller *pcie_init(struct pcie_device *dev)
 	if (link_cap & PCI_EXP_LNKCAP_DLLLARC)
 		ctrl->link_active_reporting = 1;
 
-	/* Clear all remaining event bits in Slot Status register */
+	/*
+	 * Clear all remaining event bits in Slot Status register except
+	 * Presence Detect Changed. We want to make sure possible
+	 * hotplug event is triggered when the interrupt is unmasked so
+	 * that we don't lose that event.
+	 */
 	pcie_capability_write_word(pdev, PCI_EXP_SLTSTA,
 		PCI_EXP_SLTSTA_ABP | PCI_EXP_SLTSTA_PFD |
-		PCI_EXP_SLTSTA_MRLSC | PCI_EXP_SLTSTA_PDC |
-		PCI_EXP_SLTSTA_CC | PCI_EXP_SLTSTA_DLLSC);
+		PCI_EXP_SLTSTA_MRLSC | PCI_EXP_SLTSTA_CC |
+		PCI_EXP_SLTSTA_DLLSC);
 
 	ctrl_info(ctrl, "Slot #%d AttnBtn%c PwrCtrl%c MRL%c AttnInd%c PwrInd%c HotPlug%c Surprise%c Interlock%c NoCompl%c LLActRep%c\n",
 		(slot_cap & PCI_EXP_SLTCAP_PSN) >> 19,