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

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Message-ID: <CALzav=eGXp3uHxRytfsKQdrtAV8xg8teoAs9n_sggqdAp_Hznw@mail.gmail.com>
Date: Fri, 3 Oct 2025 09:27:21 -0700
From: David Matlack <dmatlack@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: 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>, 
	Vipin Sharma <vipinsh@...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 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.