linux-kernel - Re: [PATCH v2 03/10] PCI/LUO: Forward prepare()/freeze()/cancel() callbacks to driver

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Message-ID: <CAHVum0caxqVdKfoXNLa92NFEBLwTbLCRgbH6y6kvnsWQPgcbwA@mail.gmail.com>
Date: Fri, 3 Oct 2025 09:41:49 -0700
From: Vipin Sharma <vipinsh@...gle.com>
To: David Matlack <dmatlack@...gle.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>, Chris Li <chrisl@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Len Brown <lenb@...nel.org>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org, 
	Pasha Tatashin <tatashin@...gle.com>, Jason Miu <jasonmiu@...gle.com>, 
	Saeed Mahameed <saeedm@...dia.com>, Adithya Jayachandran <ajayachandra@...dia.com>, 
	Parav Pandit <parav@...dia.com>, William Tu <witu@...dia.com>, Mike Rapoport <rppt@...nel.org>, 
	Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v2 03/10] PCI/LUO: Forward prepare()/freeze()/cancel()
 callbacks to driver

On Fri, Oct 3, 2025 at 9:27 AM David Matlack <dmatlack@...gle.com> wrote:
>
> On Fri, Oct 3, 2025 at 5:06 AM Jason Gunthorpe <jgg@...pe.ca> wrote:
> >
> > On Thu, Oct 02, 2025 at 10:24:59PM -0700, Chris Li wrote:
> >
> > > As David pointed out in the other email, the PCI also supports other
> > > non vfio PCI devices which do not have the FD and FD related sessions.
> > > That is the original intent for the LUO PCI subsystem.
> >
> > This doesn't make sense. We don't know how to solve this problem yet,
> > but I'm pretty confident we will need to inject a FD and session into
> > these drivers too.
>
> Google's LUO PCI subsystem (i.e. this series) predated a lot of the
> discussion about FD preservation and needed to support the legacy vfio
> container/group model. Outside of vfio-pci, the only other drivers
> that participate are the PF drivers (pci-pf-stub and idpf), but they
> just register empty callbacks.
>
> So from an upstream perspective we don't really have a usecase for
> callbacks. Chris ,I saw in your other email that you agree with
> dropping them in the next version, so it sounds like we are aligned
> then.
>
> Vipin Sharma is working on the vfio-pci MVP series. Vipin, if you
> anticipate VFIO is going to need driver callbacks on top of the LUO FD
> callbacks, please chime in here.

Currently, LUO FD callbacks are the only ones I need. I think we are
fine for now without PCI callbacks. I will have better clarity next
week but for now I am only using LUO FD callbacks.