PCI: pciehp: Wait for PDS if in-band presence is disabled

When in-band presence detect is disabled, PDS may come up at any time or
not at all.  PDS being low may indicate that the card is still mating, and
we could expect contact bounce to bring down the link as well.

It is reasonable to assume that most cards will mate in a hotplug slot in
about a second.  Thus, when we know PDS only reflects out-of-band presence
detect, it's worthwhile to wait the extra second or so to make sure the
card is properly mated before loading the driver and to prevent the hotplug
code from disabling a device if the presence detect change goes active
after the device is enabled.

Link: https://lore.kernel.org/r/20191025190047.38130-3-stuart.w.hayes@gmail.com
[bhelgaas: use ctrl_info() instead of pci_info()]
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>

drivers/pci/hotplug/pciehp_hpc.c

@@ -252,6 +252,22 @@ static bool pci_bus_check_dev(struct pci_bus *bus, int devfn)
 	return found;
 }
 
+static void pcie_wait_for_presence(struct pci_dev *pdev)
+{
+	int timeout = 1250;
+	u16 slot_status;
+
+	do {
+		pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
+		if (slot_status & PCI_EXP_SLTSTA_PDS)
+			return;
+		msleep(10);
+		timeout -= 10;
+	} while (timeout > 0);
+
+	pci_info(pdev, "Timeout waiting for Presence Detect\n");
+}
+
 int pciehp_check_link_status(struct controller *ctrl)
 {
 	struct pci_dev *pdev = ctrl_dev(ctrl);
@@ -261,6 +277,9 @@ int pciehp_check_link_status(struct controller *ctrl)
 	if (!pcie_wait_for_link(pdev, true))
 		return -1;
 
+	if (ctrl->inband_presence_disabled)
+		pcie_wait_for_presence(pdev);
+
 	found = pci_bus_check_dev(ctrl->pcie->port->subordinate,
 					PCI_DEVFN(0, 0));