[PATCH kernel] powerpc/powernv: Update comment about shifting IOV BAR

[David Laight]

From: Benjamin Herrenschmidt
> Sent: 14 September 2017 04:40
> On Thu, 2017-09-14 at 13:18 +1000, Alexey Kardashevskiy wrote:
> > On 14/09/17 13:07, Benjamin Herrenschmidt wrote:
> > > On Thu, 2017-09-14 at 12:45 +1000, Alexey Kardashevskiy wrote:
> > > > On 31/08/17 13:34, Alexey Kardashevskiy wrote:
> > > > > From: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> > > >
> > > > Oops, this was not right :)
> > > >
> > > > Anyway, Ben, please comment. Thanks.
> > >
> > > This is incorrect, we can do hotplug behind switches afaik.
> >
> > Do we have an actual system which allows this?
> 
> Tuleta no ?

You can logically 'hotplug' PCI(e) on any system [1].

The 'problem' is that whatever enumerates the PCI(e) at system
powerup doesn't normally assign extra resources to bridges to allow
for devices that aren't present at boot time.
So you can normally only replace cards with ones that use the same
(or less) resources, or that are not behind any bridges.
This is problematic if you have a docking station connected via
a bridge.

[1] Apart from some annoying x86 Dell servers we have which generate
an NMI when the PCIe link goes down (when we reprogram the fpga).
They also fail to boot if a link doesn't come up...

	David