Re: [PATCH v13 22/22] docs: vfio: Add vfio device cdev description

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Jun 28, 2023 at 12:56:40AM +0000, Liu, Yi L wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Wednesday, June 28, 2023 12:12 AM
> > 
> > On Tue, Jun 27, 2023 at 08:54:33AM +0000, Liu, Yi L wrote:
> > > > From: Alex Williamson <alex.williamson@redhat.com>
> > > > Sent: Thursday, June 22, 2023 5:54 AM
> > > >
> > > > On Fri, 16 Jun 2023 02:39:46 -0700
> > > > Yi Liu <yi.l.liu@intel.com> wrote:
> > >
> > > > > +VFIO device cdev doesn't rely on VFIO group/container/iommu drivers.
> > > > > +Hence those modules can be fully compiled out in an environment
> > > > > +where no legacy VFIO application exists.
> > > > > +
> > > > > +So far SPAPR does not support IOMMUFD yet.  So it cannot support device
> > > > > +cdev either.
> > > >
> > > > Why isn´t this enforced via Kconfig?  At the vfio level we could simply
> > > > add the following in patch 17/:
> > > >
> > > > config VFIO_DEVICE_CDEV
> > > >         bool "Support for the VFIO cdev /dev/vfio/devices/vfioX"
> > > >         depends on IOMMUFD && !SPAPR_TCE_IOMMU
> > > >                            ^^^^^^^^^^^^^^^^^^^
> > > >
> 
> Proposal A.
> 
> > > > Or if Jason wants, IOMMUFD could depend on !SPAPR_TCE_IOMMU for now and
> > > > the existing Kconfig options would exclude it.  If we know it doesn't
> > > > work, let's not put the burden on the user to figure that out.  A
> > > > follow-up patch for this would be fine if there's no other reason to
> > > > respin the series.
> 
> Proposal B.
> 
> > >
> > > @Jason,
> > > How about your opinion? Seems reasonable to make IOMMUFD
> > > depend on !SPAPR_TCE_IOMMU. Is it?
> > 
> > The right kconfig would be to list all the iommu drivers that can
> > support iommufd and allow it to be selected if any of them are
> > enabled.
> > 
> > This seems too complex to bother with, so I like Alex's version above..
> 
> Sorry, I'm not quite clear. Alex has two proposals above (A and B). Which
> one do you mean? It looks like you prefer A. is it? :-)

A

Jason