PCI: pciehp: Prioritize data-link event over presence detect

If Slot Status indicates changes in both Data Link Layer Status and
Presence Detect, prioritize the Link status change.

When both events are observed, pciehp currently relies on the Slot Status
Presence Detect State (PDS) to agree with the Link Status Data Link Layer
Active status.  The Presence Detect State, however, may be set to 1 through
out-of-band presence detect even if the link is down, which creates
conflicting events.

Since the Link Status accurately reflects the reachability of the
downstream bus, the Link Status event should take precedence over a
Presence Detect event.  Skip checking the PDC status if we handled a link
event in the same handler.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Keith Busch <keith.busch@intel.com>

drivers/pci/hotplug/pciehp_hpc.c

@@ -620,8 +620,18 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
 		pciehp_queue_interrupt_event(slot, INT_BUTTON_PRESS);
 	}
 
-	/* Check Presence Detect Changed */
-	if (events & PCI_EXP_SLTSTA_PDC) {
+	/*
+	 * Check Link Status Changed at higher precedence than Presence
+	 * Detect Changed.  The PDS value may be set to "card present" from
+	 * out-of-band detection, which may be in conflict with a Link Down
+	 * and cause the wrong event to queue.
+	 */
+	if (events & PCI_EXP_SLTSTA_DLLSC) {
+		ctrl_info(ctrl, "Slot(%s): Link %s\n", slot_name(slot),
+			  link ? "Up" : "Down");
+		pciehp_queue_interrupt_event(slot, link ? INT_LINK_UP :
+					     INT_LINK_DOWN);
+	} else if (events & PCI_EXP_SLTSTA_PDC) {
 		present = !!(status & PCI_EXP_SLTSTA_PDS);
 		ctrl_info(ctrl, "Slot(%s): Card %spresent\n", slot_name(slot),
 			  present ? "" : "not ");
@@ -636,13 +646,6 @@ static irqreturn_t pciehp_isr(int irq, void *dev_id)
 		pciehp_queue_interrupt_event(slot, INT_POWER_FAULT);
 	}
 
-	if (events & PCI_EXP_SLTSTA_DLLSC) {
-		ctrl_info(ctrl, "Slot(%s): Link %s\n", slot_name(slot),
-			  link ? "Up" : "Down");
-		pciehp_queue_interrupt_event(slot, link ? INT_LINK_UP :
-					     INT_LINK_DOWN);
-	}
-
 	return IRQ_HANDLED;
 }