[Intel-gfx] [PATCH v13 22/22] docs: vfio: Add vfio device cdev description

[Liu, Yi L]

> From: Alex Williamson <alex.williamson at redhat.com>
> Sent: Wednesday, June 28, 2023 1:35 AM

[The Cc list gets broken in the reply from Alex to Jason, here I reply to
Alex's email with the Cc list fixed. @Alex, seems like the same symptom
with last time, do you have any idea on it?]

> On Tue, 27 Jun 2023 13:12:14 -0300
> Jason Gunthorpe <jgg at nvidia.com> wrote:
> 
> > On Tue, Jun 27, 2023 at 08:54:33AM +0000, Liu, Yi L wrote:
> > > > From: Alex Williamson <alex.williamson at redhat.com>
> > > > Sent: Thursday, June 22, 2023 5:54 AM
> > > >
> > > > On Fri, 16 Jun 2023 02:39:46 -0700
> > > > Yi Liu <yi.l.liu at 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
> > > >                            ^^^^^^^^^^^^^^^^^^^
> > > >
> > > > 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.
> > >
> > > @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..
> >
> > > > Otherwise the series is looking pretty good to me.  It still requires
> > > > some reviews/acks in the iommufd space and it would be good to see more
> > > > reviews for the remainder given the amount of collaboration here.
> > > >
> > > > I'm out for the rest of the week, but I'll leave open accepting this
> > > > and the hot-reset series next week for the merge window.  Thanks,
> > >
> > > @Alex,
> > > Given Jason's remarks on cdev v12, I've already got a new version as below.
> > > I can post it once the above kconfig open is closed.
> >
> > I think we don't need to bend the rules, Linus would not be happy to
> > see 30 major patches that never hit linux-next at all.
> >
> > I'm happy if we put it on a branch at RC1 and merge it to the vfio &
> > iommufd trees, it is functionally the same outcome in the same time
> > frame.
> 
> Not sure I'm clear on the plan.  My intention would have been to apply
> v14 to my next branch, make sure it did see linux-next exposure,
> and send a pull request for rc1 next week.
> 
> Are you suggesting a post-merge-window pull request for v6.5 (also
> frowned on) or are you suggesting that it simmers in both our next
> branches until v6.6?  Thanks,

It appears to me the latter one. When 6.5-rc1 is released, we immediately
apply the hot-reset and cdev series onto it and put it in a shared tree to
assist the other iommufd feature development (e.g. nesting). Jason, is it?

Regards,
Yi Liu