PCI: pciehp: Enable link state change notifications

Enable the Link state notifications unconditionally. Enable the
presence detection notification only if attention button is absent.
This was discussed at this thread:
    https://lkml.kernel.org/r/529E5C0E.80903@gmail.comSigned-off-by: Rajat Jain <rajatxjain@gmail.com>
Signed-off-by: Rajat Jain <rajatjain@juniper.net>
Signed-off-by: Guenter Roeck <groeck@juniper.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/hotplug/pciehp_hpc.c

@@ -600,9 +600,17 @@ void pcie_enable_notification(struct controller *ctrl)
 	 * when it is cleared in the interrupt service routine, and
 	 * next power fault detected interrupt was notified again.
 	 */
-	cmd = PCI_EXP_SLTCTL_PDCE;
+
+	/*
+	 * Always enable link events: thus link-up and link-down shall
+	 * always be treated as hotplug and unplug respectively. Enable
+	 * presence detect only if Attention Button is not present.
+	 */
+	cmd = PCI_EXP_SLTCTL_DLLSCE;
 	if (ATTN_BUTTN(ctrl))
 		cmd |= PCI_EXP_SLTCTL_ABPE;
+	else
+		cmd |= PCI_EXP_SLTCTL_PDCE;
 	if (MRL_SENS(ctrl))
 		cmd |= PCI_EXP_SLTCTL_MRLSCE;
 	if (!pciehp_poll_mode)
@@ -610,7 +618,8 @@ void pcie_enable_notification(struct controller *ctrl)
 
 	mask = (PCI_EXP_SLTCTL_PDCE | PCI_EXP_SLTCTL_ABPE |
 		PCI_EXP_SLTCTL_MRLSCE | PCI_EXP_SLTCTL_PFDE |
-		PCI_EXP_SLTCTL_HPIE | PCI_EXP_SLTCTL_CCIE);
+		PCI_EXP_SLTCTL_HPIE | PCI_EXP_SLTCTL_CCIE |
+		PCI_EXP_SLTCTL_DLLSCE);
 
 	pcie_write_cmd(ctrl, cmd, mask);
 }