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authorLukas Wunner <lukas@wunner.de>2018-07-20 00:27:49 +0200
committerBjorn Helgaas <helgaas@kernel.org>2018-07-24 00:04:16 +0200
commit6c35a1ac3da63a7fe5b18b435a5a9d6b9fd3990a (patch)
treeeb58e8ab144026e6dbd1b30b9acdabb6ace6ca7e /drivers/pci/hotplug
parentPCI: pciehp: Declare pciehp_enable/disable_slot() static (diff)
downloadlinux-6c35a1ac3da63a7fe5b18b435a5a9d6b9fd3990a.tar.xz
linux-6c35a1ac3da63a7fe5b18b435a5a9d6b9fd3990a.zip
PCI: pciehp: Tolerate initially unstable link
When a device is hotplugged, Presence Detect and Link Up events often do not occur simultaneously, but with a lag of a few milliseconds. Only the first event received is relevant, the other one can be disregarded. Moreover, Stefan Roese reports that on certain platforms, Link State and Presence Detect may flap for up to 100 ms before stabilizing, suggesting that such events should be disregarded for at least this long: https://lkml.kernel.org/r/20180130084121.18653-1-sr@denx.de On slot enablement, pciehp_check_link_status() waits for 100 ms per PCIe r4.0, sec 6.7.3.3, then probes the hotplugged device's vendor register for up to 1 second. If this succeeds, the link is definitely up, so ignore any Presence Detect or Link State events that occurred up to this point. pciehp_check_link_status() then checks the Link Training bit in the Link Status register. This is the final opportunity to detect inaccessibility of the device and abort slot enablement. Any link or presence change that occurs afterwards will cause the slot to be disabled again immediately after attempting to enable it. The astute reviewer may appreciate that achieving this behavior would be more complicated had pciehp not just been converted to enable/disable the slot exclusively from the IRQ thread: When the slot is enabled via sysfs, each link or presence flap would otherwise cause the IRQ thread to run and it would have to sense that those events are belonging to a concurrent slot enablement operation and disregard them. It would be much more difficult than this mere 3 line change. Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Cc: Stefan Roese <sr@denx.de>
Diffstat (limited to 'drivers/pci/hotplug')
-rw-r--r--drivers/pci/hotplug/pciehp_hpc.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 7f1a29cd6a17..6b8350a3875c 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -270,6 +270,11 @@ int pciehp_check_link_status(struct controller *ctrl)
found = pci_bus_check_dev(ctrl->pcie->port->subordinate,
PCI_DEVFN(0, 0));
+ /* ignore link or presence changes up to this point */
+ if (found)
+ atomic_and(~(PCI_EXP_SLTSTA_DLLSC | PCI_EXP_SLTSTA_PDC),
+ &ctrl->pending_events);
+
pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
ctrl_dbg(ctrl, "%s: lnk_status = %x\n", __func__, lnk_status);
if ((lnk_status & PCI_EXP_LNKSTA_LT) ||