[PATCH v4 3/8] PCI: Don't block runtime PM for Thunderbolt host hotplug ports

[Lukas Wunner]

Hotplug ports generally block their parents from suspending to D3hot as
otherwise their interrupts couldn't be delivered.

An exception are Thunderbolt host controllers:  They have a separate
GPIO pin to side-band signal plug events even if the controller is
powered down or its parent ports are suspended to D3.  They can be told
apart from Thunderbolt controllers in attached devices by checking if
they're situated below a non-Thunderbolt device (typically a root port,
or the downstream port of a PCIe switch in the case of the MacPro6,1).

To enable runtime PM for Thunderbolt on the Mac, the downstream bridges
of a host controller must not block runtime PM on the upstream bridge as
power to the chip is only cut once the upstream bridge has suspended.
Amend the condition in pci_dev_check_d3cold() accordingly.

Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Andreas Noever <andreas.noever@xxxxxxxxx>
Cc: Tomas Winkler <tomas.winkler@xxxxxxxxx>
Cc: Amir Levy <amir.jer.levy@xxxxxxxxx>
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
---
 drivers/pci/pci.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8ed098d..0b03fe7 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2271,6 +2271,7 @@ bool pci_bridge_d3_possible(struct pci_dev *bridge)
 
 static int pci_dev_check_d3cold(struct pci_dev *dev, void *data)
 {
+	struct pci_dev *parent, *grandparent;
 	bool *d3cold_ok = data;
 
 	if (/* The device needs to be allowed to go D3cold ... */
@@ -2284,7 +2285,17 @@ static int pci_dev_check_d3cold(struct pci_dev *dev, void *data)
 	    !pci_power_manageable(dev) ||
 
 	    /* Hotplug interrupts cannot be delivered if the link is down. */
-	    dev->is_hotplug_bridge)
+	    (dev->is_hotplug_bridge &&
+
+		/*
+		 * Exception:  Thunderbolt host controllers have a pin to
+		 * side-band signal plug events.  Their hotplug ports are
+		 * recognizable by having a non-Thunderbolt device as
+		 * grandparent.
+		 */
+		!(dev->is_thunderbolt && (parent = pci_upstream_bridge(dev)) &&
+				 (grandparent = pci_upstream_bridge(parent)) &&
+						!grandparent->is_thunderbolt)))
 
 		*d3cold_ok = false;
 
-- 
2.11.0