[PATCH] PCI: pciehp: Don't enable slot unless link or presence up

[Stuart Hayes <stuart.w.hayes@gmail.com>]

When a pciehp slot is powered down via /sys/bus/pci/slots/<slot>/power,
and then the card is physically removed, the kernel will sometimes try to
enable the slot as the card is removed, which results in an error in the
kernel log.

This can happen if the presence detect and link active bits don't go down
at the exact same time. When the card is disabled via /sys/.../power, the
card is placed in OFF_STATE, but the presence detect and link active bits
can still be up.  Then, when, say, presence detect goes down, an interrupt
reports that the presence detect has changed, and the code in
pciehp_handle_presence_or_link_change() will see that the link is up
(because it hasn't gone down yet), and it will try to enable the slot.

This patch modifies that code so it won't try to enable a slot in OFF_STATE
unless it sees the presence detect changed bit with presence detect active,
or the link status changed bit with an active link. This will prevent the
unwanted attempts to enable a card that's being removed, but will still
allow the slot to come up if the slot is re-enabled by writing to
/sys/.../power, or if a new card is added to the slot.

Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
---
 drivers/pci/hotplug/pciehp_ctrl.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
index 6503d15effbb..f6cbf21711e0 100644
--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -267,16 +267,20 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
 		cancel_delayed_work(&ctrl->button_work);
 		/* fall through */
 	case OFF_STATE:
-		ctrl->state = POWERON_STATE;
-		mutex_unlock(&ctrl->state_lock);
-		if (present)
-			ctrl_info(ctrl, "Slot(%s): Card present\n",
-				  slot_name(ctrl));
-		if (link_active)
-			ctrl_info(ctrl, "Slot(%s): Link Up\n",
-				  slot_name(ctrl));
-		ctrl->request_result = pciehp_enable_slot(ctrl);
-		break;
+		if ((events & PCI_EXP_SLTSTA_PDC && present) ||
+		    (events & PCI_EXP_SLTSTA_DLLSC && link_active)) {
+			ctrl->state = POWERON_STATE;
+			mutex_unlock(&ctrl->state_lock);
+			if (present)
+				ctrl_info(ctrl, "Slot(%s): Card present\n",
+					  slot_name(ctrl));
+			if (link_active)
+				ctrl_info(ctrl, "Slot(%s): Link Up\n",
+					  slot_name(ctrl));
+			ctrl->request_result = pciehp_enable_slot(ctrl);
+			break;
+		}
+		/* fall through */
 	default:
 		mutex_unlock(&ctrl->state_lock);
 		break;
-- 
2.18.1