diff mbox series

[v2,2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

Message ID 20191011205127.4884-3-stuart.w.hayes@gmail.com
State Superseded
Delegated to: Bjorn Helgaas
Headers show
Series PCI: pciehp: Do not turn off slot if presence comes up after link | expand

Commit Message

Stuart Hayes Oct. 11, 2019, 8:51 p.m. UTC 
From: 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 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@gmail.com>
Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
---
v2:
  replace while(true) loop with do...while

 drivers/pci/hotplug/pciehp_hpc.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

Comments

Andy Shevchenko Oct. 12, 2019, 7:34 a.m. UTC | #1 
On Fri, Oct 11, 2019 at 11:51 PM Stuart Hayes <stuart.w.hayes@gmail.com> wrote:
>
> From: 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 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.

Thank you!
My comments below.

> +static void pcie_wait_for_presence(struct pci_dev *pdev)
> +{
> +       int timeout = 1250;

> +       bool pds;

make W=1 will issue a warning. Just remove the line.

> +       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, "Presence Detect state not set in 1250 msec\n");

Perhaps ("%d", timeout) ?

> +}
diff mbox series

Patch

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index dc109d521f30..db5c7b082fda 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -242,6 +242,23 @@  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;
+	bool pds;
+	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, "Presence Detect state not set in 1250 msec\n");
+}
+
 int pciehp_check_link_status(struct controller *ctrl)
 {
 	struct pci_dev *pdev = ctrl_dev(ctrl);
@@ -251,6 +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));