Re: [PATCH 8/9] vfio/pci: export nvlink2 support into vendor vfio_pci drivers

[Max Gurtovoy]

On 3/11/2021 9:54 AM, Alexey Kardashevskiy wrote:
> On 11/03/2021 13:00, Jason Gunthorpe wrote:
> > On Thu, Mar 11, 2021 at 12:42:56PM +1100, Alexey Kardashevskiy wrote:
> > > > > btw can the id list have only vendor ids and not have device ids?
> > > >
> > > > The PCI matcher is quite flexable, see the other patch from Max for
> > > > the igd
> > >   ah cool, do this for NVIDIA GPUs then please, I just discovered 
> > > another P9
> > > system sold with NVIDIA T4s which is not in your list.
> >
> > I think it will make things easier down the road if you maintain an
> > exact list <shrug>
>
>
> Then why do not you do the exact list for Intel IGD? The commit log 
> does not explain this detail.

I expect Intel team to review this series and give a more precise list.

I did the best I could in finding a proper configuration for igd.


> > > > But best practice is to be as narrow as possible as I hope this will
> > > > eventually impact module autoloading and other details.
> > >
> > > The amount of device specific knowledge is too little to tie it up 
> > > to device
> > > ids, it is a generic PCI driver with quirks. We do not have a separate
> > > drivers for the hardware which requires quirks.
> >
> > It provides its own capability structure exposed to userspace, that is
> > absolutely not a "quirk"
> >
> > > And how do you hope this should impact autoloading?
> >
> > I would like to autoload the most specific vfio driver for the target
> > hardware.
>
>
> Is there an idea how it is going to work? For example, the Intel IGD 
> driver and vfio-pci-igd - how should the system pick one? If there is 
> no MODULE_DEVICE_TABLE in vfio-pci-xxx, is the user supposed to try 
> binding all vfio-pci-xxx drivers until some binds?

For example, in my local setup I did a POC patch that convert some 
drivers to be "manual binding only drivers".

So the IGD driver will have the priority, user will unbind the device 
from it, load igd-vfio-pci, bind the device to it, ends with probing.

For now we separated the driver core stuff until we all agree that this 
series is the right way to go + we also make sure it's backward compatible.

> > If you someday need to support new GPU HW that needs a different VFIO
> > driver then you are really stuck because things become indeterminate
> > if there are two devices claiming the ID. We don't have the concept of
> > "best match", driver core works on exact match.