Re: [PATCH v4 1/2] xen-pciback: prepare for the split for stub and PV

[Juergen Gross <jgross@xxxxxxxx>]

On 27.09.21 09:35, Oleksandr Andrushchenko wrote:
> On 27.09.21 10:26, Jan Beulich wrote:
> > On 27.09.2021 08:58, Oleksandr Andrushchenko wrote:
> > > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > >
> > > Currently PCI backend implements multiple functionalities at a time.
> > > To name a few:
> > > 1. It is used as a database for assignable PCI devices, e.g. xl
> > >      pci-assignable-{add|remove|list} manipulates that list. So, whenever
> > >      the toolstack needs to know which PCI devices can be passed through
> > >      it reads that from the relevant sysfs entries of the pciback.
> > > 2. It is used to hold the unbound PCI devices list, e.g. when passing
> > >      through a PCI device it needs to be unbound from the relevant device
> > >      driver and bound to pciback (strictly speaking it is not required
> > >      that the device is bound to pciback, but pciback is again used as a
> > >      database of the passed through PCI devices, so we can re-bind the
> > >      devices back to their original drivers when guest domain shuts down)
> > > 3. Device reset for the devices being passed through
> > > 4. Para-virtualised use-cases support
> > >
> > > The para-virtualised part of the driver is not always needed as some
> > > architectures, e.g. Arm or x86 PVH Dom0, are not using backend-frontend
> > > model for PCI device passthrough. For such use-cases make the very
> > > first step in splitting the xen-pciback driver into two parts: Xen
> > > PCI stub and PCI PV backend drivers.
> > >
> > > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > >
> > > ---
> > > Changes since v3:
> > > - Move CONFIG_XEN_PCIDEV_STUB to the second patch
> > I'm afraid this wasn't fully done:
> >
> > > --- a/drivers/xen/xen-pciback/Makefile
> > > +++ b/drivers/xen/xen-pciback/Makefile
> > > @@ -1,5 +1,6 @@
> > >    # SPDX-License-Identifier: GPL-2.0
> > >    obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o
> > > +obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o
> > While benign when added here, this addition still doesn't seem to
> > belong here.
> My bad. So, it seems without CONFIG_XEN_PCIDEV_STUB the change seems
>
> to be non-functional. With CONFIG_XEN_PCIDEV_STUB we fail to build on 32-bit
>
> architectures...
>
> What would be the preference here? Stefano suggested that we still define
>
> CONFIG_XEN_PCIDEV_STUB, but in disabled state, e.g. we add tristate to it
>
> in the second patch
>
> Another option is just to squash the two patches.
Squashing would be fine for me.


Juergen

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