[PATCH] PCI: Do not use pcie_get_speed_cap() to determine when to start waiting

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Kai-Heng Feng reported that it takes long time (>1s) to resume
Thunderbolt connected PCIe devices from both runtime suspend and system
sleep (s2idle).

These PCIe downstream ports the second link capability (PCI_EXP_LNKCAP2)
announces support for speeds > 5 GT/s but it is then capped by the
second link control (PCI_EXP_LNKCTL2) register to 2.5 GT/s. This
possiblity was not considered in pci_bridge_wait_for_secondary_bus() so
it ended up waiting for 1100 ms as these ports do not support active
link layer reporting either.

PCIe spec 5.0 section 6.6.1 mandates that we must wait minimum of 100 ms
before sending configuration request to the device below, if the port
does not support speeds > 5 GT/s, and if it does we first need to wait
for the data link layer to become active before waiting for that 100 ms.

PCIe spec 5.0 section 7.5.3.6 further says that all downstream ports
that support speeds > 5 GT/s must support active link layer reporting so
instead of looking for the speed we can check for the active link layer
reporting capability and determine how to wait based on that (as they go
hand in hand).

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206837
Reported-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
 drivers/pci/pci.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 595fcf59843f..d9d9ff5b968e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4822,7 +4822,13 @@ void pci_bridge_wait_for_secondary_bus(struct pci_dev *dev)
 	if (!pcie_downstream_port(dev))
 		return;
 
-	if (pcie_get_speed_cap(dev) <= PCIE_SPEED_5_0GT) {
+	/*
+	 * Since PCIe spec mandates that all downstream ports that support
+	 * speeds greater than 5 GT/s must support data link layer active
+	 * reporting so we use that here to determine when the delay should
+	 * be issued.
+	 */
+	if (!dev->link_active_reporting) {
 		pci_dbg(dev, "waiting %d ms for downstream link\n", delay);
 		msleep(delay);
 	} else {
-- 
2.25.1