linux-kernel - [PATCH v4 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

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Date:   Fri, 25 Oct 2019 15:00:46 -0400
From:   Stuart Hayes <stuart.w.hayes@...il.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Austin Bolen <austin_bolen@...l.com>, keith.busch@...el.com,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, lukas@...ner.de,
        Stuart Hayes <stuart.w.hayes@...il.com>
Subject: [PATCH v4 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

From: Alexandru Gagniuc <mr.nuke.me@...il.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 about a second. Thus, when we know PDS only reflects out-of-band
presence, 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.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>
Signed-off-by: Stuart Hayes <stuart.w.hayes@...il.com>
---
v2:
  replace while(true) loop with do...while
v3
  remove unused variable declaration (pds)
  modify text of warning message
v4
  remove "!!" boolean conversion from "if" condition for readability

 drivers/pci/hotplug/pciehp_hpc.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index dc109d521f30..02d95ab27a12 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -242,6 +242,22 @@ 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 state to be set\n");
+}
+
 int pciehp_check_link_status(struct controller *ctrl)
 {
 	struct pci_dev *pdev = ctrl_dev(ctrl);
@@ -251,6 +267,9 @@ 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));
 
-- 
2.18.1