Re: PSA: migrating linux-hotplug to new vger infrastructure

On Mon, Nov 6, 2023 at 11:25=E2=80=AFAM Greg KH <[email protected]=
> wrote:
>
> On Mon, Nov 06, 2023 at 11:05:47AM -0800, Eric Pilmore wrote:
> > On Mon, Nov 6, 2023 at 5:44=E2=80=AFAM 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.

Special MMIO reservation in BIOS is not required if a device in your
PCIe tree, such as a Broadcom Gen4 or Gen5 switch device, can reserve
address space via "synthetic mode" for missing devices.

Matt


--=20
Matthew Dharm
Former Maintainer, USB Mass Storage driver for Linux