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Date:   Mon, 6 Nov 2023 20:25:34 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Eric Pilmore <epilmore@gigaio.com>
Cc:     Konstantin Ryabitsev <konstantin@linuxfoundation.org>,
        linux-hotplug@vger.kernel.org, D Meyer <dmeyer@gigaio.com>
Subject: Re: PSA: migrating linux-hotplug to new vger infrastructure
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On Mon, Nov 06, 2023 at 11:05:47AM -0800, Eric Pilmore wrote:
> On Mon, Nov 6, 2023 at 5:44 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> >
> > I think the list can just be deleted, there's no traffic anymore, and
> > "hotplug" doesn't make any sense anymore as "everything" can be
> > added/removed from a Linux system these days.
> >
> > So can we just remove it?
> >
> > thanks,
> >
> > greg k-h
> 
> Hi Greg,
> 
> I was curious about your comment regarding "everything". Is it
> possible to dynamically add/remove entire I/O sub-trees on the PCIe
> side?

It has for decades.  Well, PCIe isn't decades old, but this has worked
for PCI systems for decades.

> In other words, can a PCIe bridge, and all associated
> sub-branches be dynamically added/removed?

Again, yes, for a very long time.  If your hardware supports it.

> If so, is there special BIOS support required for possibly reserving
> adequate MMIO address space?

Yes.  That's what those types of systems do, this is nothing new at all,
we had this working in Linux in 2002 or so.  You need special hardware
to support this, and USB4/Thunderbolt is bringing this for more common
hardware as well.

thanks,

greg k-h