Re: [PATCH v3 2/4] PCI/portdrv: Add necessary wait for disabling hotplug events

[Lukas Wunner <lukas@wunner.de>]

On Fri, Feb 28, 2025 at 02:29:29PM +0800, Feng Tang wrote:
> On Tue, Feb 25, 2025 at 12:42:04PM +0800, Feng Tang wrote:
> > > > There might be some misunderstaning here :), I responded in
> > > > https://lore.kernel.org/lkml/Z6LRAozZm1UfgjqT@U-2FWC9VHC-2323.local/
> > > > that your suggestion could solve our issue.
> > > 
> > > Well, could you test it please?
> > 
> We just tried the patch on the hardware and initial 5.10 kernel, and
> the problem cannot be reproduced, as the first PCIe hotplug command
> of disabling CCIE and HPIE was not issued.

Good!

> Should I post a new version patch with your suggestion?

Yes, please.

> Also I would like to separate this patch from the patch dealing the
> nomsi irq storm issue. How do you think?

Makes sense to me.

The problem with the nomsi irq storm is really that if the platform
(i.e. BIOS) doesn't grant OSPM control of hotplug, OSPM (i.e. the kernel)
cannot modify hotplug registers because the assumption is that the
platform controls them.  If the platform doesn't actually handle
hotplug, but keeps the interrupts enabled, that's basically a bug
of the specific platform.

I think the kernel community's stance in such situations is that the
BIOS vendor should provide an update with a fix.  In some cases
that's not posible because the product is no longer supported,
or the vendor doesn't care about Linux issues because it only
supports Windows or macOS.  In those cases, we deal with these
problems with a quirk.  E.g. on x86 we often use a DMI quirk to
recognize affected hardware and the quirk would then disable the
hotplug interrupts.

Thanks,

Lukas