[PATCH v3 3/4] PCI: hotplug: Wait for PDS when in-band presence is disabled

[Alexandru Gagniuc <mr.nuke.me@gmail.com>]

When inband presence 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 less than a second. Thus, when we know PDS only reflects
out-of-band presence, it's worthwhile to wait the extra second and
make sure the card is properly mated before loading the driver.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
---
 drivers/pci/hotplug/pciehp_hpc.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 078d78a7437d..6cd2c4fb4edb 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -240,6 +240,25 @@ 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 = 1000;
+	bool pds;
+	u16 slot_status;
+
+	while(true) {
+		pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
+		pds = !!(slot_status & PCI_EXP_SLTSTA_PDS);
+		if (pds || timeout <= 0)
+			break;
+		msleep(10);
+		timeout -= 10;
+	}
+
+	if (!pds)
+		pci_info(pdev, "Presence Detect state not set in 1000 msec\n");
+}
+
 int pciehp_check_link_status(struct controller *ctrl)
 {
 	struct pci_dev *pdev = ctrl_dev(ctrl);
@@ -249,6 +268,9 @@ 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));
 
-- 
2.20.1