Re: [Bug 215525] New: HotPlug does not work on upstream kernel 5.17.0-rc1

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Kai-Heng]

On Fri, Jan 28, 2022 at 09:29:31AM +0100, Mariusz Tkaczyk wrote:
> On Thu, 27 Jan 2022 20:52:12 -0600
> Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Thu, Jan 27, 2022 at 03:46:15PM +0100, Mariusz Tkaczyk wrote:
> > > ...
> > > Thanks for your suggestions. Blazej did some tests and results were
> > > inconclusive. He tested it on two same platforms. On the first one
> > > it didn't work, even if he reverted all suggested patches. On the
> > > second one hotplugs always worked.
> > > 
> > > He noticed that on first platform where issue has been found
> > > initally, there was boot parameter "pci=nommconf". After adding
> > > this parameter on the second platform, hotplugs stopped working too.
> > > 
> > > Tested on tag pci-v5.17-changes. He have CONFIG_HOTPLUG_PCI_PCIE
> > > and CONFIG_DYNAMIC_DEBUG enabled in config. He also attached two
> > > dmesg logs to bugzilla with boot parameter 'dyndbg="file pciehp*
> > > +p" as requested. One with "pci=nommconf" and one without.
> > > 
> > > Issue seems to related to "pci=nommconf" and it is probably caused
> > > by change outside pciehp.  
> > 
> > Maybe I'm missing something.  If I understand correctly, the problem
> > has nothing to do with the kernel version (correct me if I'm wrong!)
> 
> The problem occurred after the merge commit. It is some kind of
> regression.

The bug report doesn't yet contain the evidence showing this.  It only
contains dmesg logs with "pci=nommconf" where pciehp doesn't work
(which is the expected behavior) and a log without "pci=nommconf"
where pciehp does work (which is again the expected behavior).

> > PCIe native hotplug doesn't work when booted with "pci=nommconf".
> > When using "pci=nommconf", obviously we can't access the extended PCI
> > config space (offset 0x100-0xfff), so none of the extended
> > capabilities are available.
> > 
> > In that case, we don't even ask the platform for control of PCIe
> > hotplug via _OSC.  From the dmesg diff from normal (working) to
> > "pci=nommconf" (not working):
> > 
> >   -Command line: BOOT_IMAGE=/boot/vmlinuz-smp ...
> >   +Command line: BOOT_IMAGE=/boot/vmlinuz-smp pci=nommconf ...
> >   ...
> >   -acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM
> > Segments MSI HPX-Type3] -acpi PNP0A08:00: _OSC: platform does not
> > support [AER LTR] -acpi PNP0A08:00: _OSC: OS now controls
> > [PCIeHotplug PME PCIeCapability] +acpi PNP0A08:00: _OSC: OS supports
> > [ASPM ClockPM Segments MSI HPX-Type3] +acpi PNP0A08:00: _OSC: not
> > requesting OS control; OS requires [ExtendedConfig ASPM ClockPM MSI]
> > +acpi PNP0A08:00: MMCONFIG is disabled, can't access extended PCI
> > configuration space under this bridge.
> 
> So, it shouldn't work from years but it has been broken recently, that
> is the only objection I have. Could you tell why it was working?
> According to your words- it shouldn't. We are using VMD driver, is that
> matter?

04b12ef163d1 ("PCI: vmd: Honor ACPI _OSC on PCIe features") looks like
a it could be related.  Try reverting that commit and see whether it
makes a difference.

Bjorn