Thank you Greg.
About the last one , it's been a while but I wasn't sure whether Linux was
going to do its own enumeration.
Of course it's best to take advantage of all the stuff done by UEFI ,
padding etc.

S

On Thu, 13 Feb 2020 at 12:48, Greg KH <greg@kroah.com> wrote:

> On Thu, Feb 13, 2020 at 12:40:59PM -0500, Sadanand Warrier wrote:
> > Hi
> >    I had  question about PCIe hotplug. We have hardware that is connected
> > to the host by means of two PCIe switches. i.e. the host sees a PCIe
> switch
> > connected to one of its buses and on the far side of that switch another
> > PCIe switch which has a PCIe device.
> >    It is possible that this device does not train its host facing PCIe
> > links before the server enumerates down its PCI bus and reaches those
> > links. It is also possible the PCIe switch to which the device is
> attached
> > has not been able to train its own links before server enumeration.
> >   Is PCIe hotplug built to work on schemes like this? Let us assume that
> > the hardware has been designed to trasmit a presence signal once the
> links
> > are trained but this could happen after the server enumeration?
>
> Look at the PCIe hotplug spec, it should answer all of your questions
> about this.
>
> >   Incidentally does the server take advantage of the BIOS/UEFI
> enumeration?
>
> Yes, of course, how else would the kernel be able to enumerate PCI
> devices?  :)
>
> thanks,
>
> greg k-h
>