PCI: pciehp: Ignore belated Presence Detect Changed caused by DPC

JIRA: https://issues.redhat.com/browse/RHEL-107597
Upstream Status: bbf10cd

commit bbf10cd
Author: Lukas Wunner <lukas@wunner.de>
Date:   Wed Jun 18 16:38:25 2025 +0200

    PCI: pciehp: Ignore belated Presence Detect Changed caused by DPC

    Commit c3be50f ("PCI: pciehp: Ignore Presence Detect Changed caused by
    DPC") sought to ignore Presence Detect Changed events occurring as a side
    effect of Downstream Port Containment.

    The commit awaits recovery from DPC and then clears events which occurred
    in the meantime.  However if the first event seen after DPC is Data Link
    Layer State Changed, only that event is cleared and not Presence Detect
    Changed.  The object of the commit is thus defeated.

    That's because pciehp_ist() computes the events to clear based on the local
    "events" variable instead of "ctrl->pending_events".  The former contains
    the events that had occurred when pciehp_ist() was entered, whereas the
    latter also contains events that have accumulated while awaiting DPC
    recovery.

    In practice, the order of PDC and DLLSC events is arbitrary and the delay
    in-between can be several milliseconds.

    So change the logic to always clear PDC events, even if they come after an
    initial DLLSC event.

    Fixes: c3be50f ("PCI: pciehp: Ignore Presence Detect Changed caused by DPC")
    Reported-by: Lương Việt Hoàng <tcm4095@gmail.com>
    Reported-by: Joel Mathew Thomas <proxy0@tutamail.com>
    Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219765#c165
    Signed-off-by: Lukas Wunner <lukas@wunner.de>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Tested-by: Lương Việt Hoàng <tcm4095@gmail.com>
    Tested-by: Joel Mathew Thomas <proxy0@tutamail.com>
    Link: https://patch.msgid.link/d9c4286a16253af7e93eaf12e076e3ef3546367a.1750257164.git.lukas@wunner.de

Signed-off-by: Myron Stowe <mstowe@redhat.com>

Author: Myron Stowe

drivers/pci/hotplug/pciehp_hpc.c

@@ -771,7 +771,7 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
 		u16 ignored_events = PCI_EXP_SLTSTA_DLLSC;
 
 		if (!ctrl->inband_presence_disabled)
-			ignored_events |= events & PCI_EXP_SLTSTA_PDC;
+			ignored_events |= PCI_EXP_SLTSTA_PDC;
 
 		events &= ~ignored_events;
 		pciehp_ignore_link_change(ctrl, pdev, irq, ignored_events);