Re: [libvirt] [PATCH 0/3] sample: vfio mdev display devices.

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 26 Apr 2018 08:14:27 +0200
Gerd Hoffmann <kraxel@redhat.com> wrote:

> On Thu, Apr 26, 2018 at 03:44:15AM +0000, Tian, Kevin wrote:
> > > From: Alex Williamson
> > > Sent: Thursday, April 19, 2018 2:32 AM
> > > 
> > > That almost begins to look reasonable, but then we can only expose this
> > > for mdev devices, what if we were to hack a back door into a directly
> > > assigned GPU that tracks the location of active display in the
> > > framebuffer and implement the GFX_PLANE interface for that?  We have no
> > > sysfs representation for either the template or the actual device for
> > > anything other than mdev.  This inconsistency with physically assigned
> > > devices has been one of my arguments against enhancing mdev sysfs.  
> > 
> > One possible option is to wrap directly assigned GPU into a mdev. The
> > parent driver could be a dummy PCI driver which does basic PCI
> > initialization, and then provide hooks for vendor-specific hack.   
> 
> Thowing amdgpu into the mix.  Looks they have vgpu support too, but
> using sriov instead of mdev.  Having VFIO_GFX support surely looks
> useful there.  Adding a mdev dependency to the VFIO_GFX api would makes
> things more complicated there for (IMHO) no good reason ...

Yes, it may be that a device wanting to implement display or migration
might take the mdev approach, but that should be a choice of the
implementation, not a requirement imposed by the API.  Thanks,

Alex