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

[Bjorn Helgaas <helgaas@kernel.org>]

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
>