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

[Blazej Kucman <blazej.kucman@linux.intel.com>]

On Wed, 9 Feb 2022 15:02:18 -0600
Bjorn Helgaas <helgaas@kernel.org> wrote:

> On Wed, Feb 09, 2022 at 02:41:02PM +0100, Blazej Kucman wrote:
> > On Thu, 3 Feb 2022 09:58:04 -0600
> > Bjorn Helgaas <helgaas@kernel.org> wrote:  
> 
> > > Why were you testing with "pci=nommconf"?  Do you think anybody
> > > uses that with VMD and NVMe?  
> > 
> > It was added long time ago when it was useful.  
> 
> I'm curious about why it was useful.  It suggests a possible MMCONFIG
> issue in firmware or in Linux.  If it was a Linux issue, ideally we
> would fix that.  If it's a firmware issue, ideally we would work
> around it or automatically turn on "pci=nommconf" so the user wouldn't
> have to figure that out.
> 

The parameter was added many years ago (project has more than 10 years)
and I don't know the reason. Probably it was useful on pre-production
platforms, for software validation. It was added to our
internal BKMs. It didn't cause any real issue in our workflow until now.

Unfortunately, I'm unable to answer more precisely.
We scheduled steps to remove it definitely from our work environment.

> > Bugzilla report can be closed if you don't consider it as
> > regression.  
> 
> OK, I closed it with the details.  I'm not entirely convinced that
> 04b12ef163d1 ("PCI: vmd: Honor ACPI _OSC on PCIe features") was the
> right thing, but I'll pursue that elsewhere.
> 
> Thanks for your patience in working through this, and sorry for the
> hassle it caused you.
> 
> Bjorn

Thanks,
Blazej