Re: [PATCH] acpi: pcihp: make pending delete expire in 5sec

[Ani Sinha <anisinha@redhat.com>]

On Tue, 4 Apr 2023, Gerd Hoffmann wrote:

>   Hi,
>
> > > Allowing pending delete expire brings ACPI PCI hotplug on par
> > > with native PCIe unplug behavior [1] which in its turn refers
> > > back to ACPI PCI hotplug ability to repeat unplug requests.
>
> > A bit concerned about how this interacts with failover,
> > and 5sec is a lot of time that I hoped we'd avoid with acpi.
> > Any better ideas of catching such misbehaving guests?
>
> The 5sec are coming from the pcie spec: The hot-unplug request can be
> canceled within 5 seconds by pressing the button again. The problem here
> is that both hotplug and hot-unplug use the same signaling path, so we
> really have to wait the 5 seconds to avoid the OS mis-interpreting the
> button press as 'cancel' event.
>
> ACPI hotplug hasn't this problem.  A unplug request is a unplug request,

For ACPI case, I think all we want is to make sure that the first unplug
event to not stick forever. A non-zero but small delay would make sure
that the first
unplug event would get cleared after that interval and subsequent unplug
events will get registered without that error.

> period.  And it can't be canceled.  So it should be possible to use a
> shorter period.  Possibly even no delay at all.
>
> take care,
>   Gerd
>
>