PCI: pciehp: Assume NoCompl+ for Thunderbolt ports

Certain Thunderbolt 1 controllers claim to support Command Completed events
(value of 0b in the No Command Completed Support field of the Slot
Capabilities register) but in reality they neither set the Command
Completed bit in the Slot Status register nor signal a Command Completed
interrupt:

  8086:1513  CV82524  [Light Ridge 4C  2010]
  8086:151a  DSL2310  [Eagle Ridge 2C  2011]
  8086:151b  CVL2510  [Light Peak 2C   2010]
  8086:1547  DSL3510  [Cactus Ridge 4C 2012]
  8086:1548  DSL3310  [Cactus Ridge 2C 2012]
  8086:1549  DSL2210  [Port Ridge 1C   2011]

All known newer chips (Redwood Ridge and onwards) set No Command Completed
Support, indicating that they do not support Command Completed events.

The user-visible impact is that after unplugging such a device, 2 seconds
elapse until pciehp is unbound.  That's because on ->remove,
pcie_write_cmd() is called via pcie_disable_notification() and every call
to pcie_write_cmd() takes 2 seconds (1 second for each invocation of
pcie_wait_cmd()):

  [  337.942727] pciehp 0000:0a:00.0:pcie204: Timeout on hotplug command 0x1038 (issued 21176 msec ago)
  [  340.014735] pciehp 0000:0a:00.0:pcie204: Timeout on hotplug command 0x0000 (issued 2072 msec ago)

That by itself has always been unpleasant, but the situation has become
worse with commit cc27b735ad3a ("PCI/portdrv: Turn off PCIe services during
shutdown"):  Now pciehp is unbound on ->shutdown.  Because Thunderbolt
controllers typically have 4 hotplug ports, every reboot and shutdown is
now delayed by 8 seconds, plus another 2 seconds for every attached
Thunderbolt 1 device.

Thunderbolt hotplug slots are not physical slots that one inserts cards
into, but rather logical hotplug slots implemented in silicon.  Devices
appear beyond those logical slots once a PCI tunnel is established on top
of the Thunderbolt Converged I/O switch.  One would expect commands written
to the Slot Control register to be executed immediately by the silicon, so
for simplicity we always assume NoCompl+ for Thunderbolt ports.

Fixes: cc27b735ad3a ("PCI/portdrv: Turn off PCIe services during shutdown")
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: stable@vger.kernel.org	# v4.12+
Cc: Sinan Kaya <okaya@codeaurora.org>
Cc: Yehezkel Bernat <yehezkel.bernat@intel.com>
Cc: Michael Jamet <michael.jamet@intel.com>
Cc: Andreas Noever <andreas.noever@gmail.com>

drivers/pci/hotplug/pciehp_hpc.c

@@ -848,6 +848,13 @@ struct controller *pcie_init(struct pcie_device *dev)
 	if (pdev->hotplug_user_indicators)
 		slot_cap &= ~(PCI_EXP_SLTCAP_AIP | PCI_EXP_SLTCAP_PIP);
 
+	/*
+	 * We assume no Thunderbolt controllers support Command Complete events,
+	 * but some controllers falsely claim they do.
+	 */
+	if (pdev->is_thunderbolt)
+		slot_cap |= PCI_EXP_SLTCAP_NCCS;
+
 	ctrl->slot_cap = slot_cap;
 	mutex_init(&ctrl->ctrl_lock);
 	init_waitqueue_head(&ctrl->queue);