[PATCH for-linus] PCI: pciehp: Ignore belated Presence Detect Changed caused by DPC

[PATCH for-linus] PCI: pciehp: Ignore belated Presence Detect Changed caused by DPC

[Lukas Wunner]

Commit c3be50f7547c ("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: c3be50f7547c ("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
Tested-by: Lương Việt Hoàng <tcm4095@gmail.com>
Tested-by: Joel Mathew Thomas <proxy0@tutamail.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
 drivers/pci/hotplug/pciehp_hpc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index ebd342b..91d2d92 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/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);
-- 
2.47.2

Re: [PATCH for-linus] PCI: pciehp: Ignore belated Presence Detect Changed caused by DPC

[Bjorn Helgaas]

On Wed, Jun 18, 2025 at 04:38:25PM +0200, Lukas Wunner wrote:
> Commit c3be50f7547c ("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: c3be50f7547c ("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
> Tested-by: Lương Việt Hoàng <tcm4095@gmail.com>
> Tested-by: Joel Mathew Thomas <proxy0@tutamail.com>
> Signed-off-by: Lukas Wunner <lukas@wunner.de>

Applied to pci/for-linus for v6.16, thanks, Lukas!

> ---
>  drivers/pci/hotplug/pciehp_hpc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index ebd342b..91d2d92 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/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);
> -- 
> 2.47.2
>