Re: [Xen-devel] [PATCH v9 12/14] tools/libxl: read from config if passing through primary GPU

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-07-03 at 15:50 +0100, Ian Campbell wrote:
> On Thu, 2014-07-03 at 11:30 +0100, Jan Beulich wrote:
> > >>> On 02.07.14 at 21:00, <linux@xxxxxxxxxxxxxx> wrote:
> > > Wednesday, July 2, 2014, 8:42:21 PM, you wrote:
> > >> --- a/docs/man/xl.cfg.pod.5
> > >> +++ b/docs/man/xl.cfg.pod.5
> > >> @@ -601,6 +601,13 @@ More information about Xen gfx_passthru feature is 
> > >> available
> > >>  on the XenVGAPassthrough L<http://wiki.xen.org/wiki/XenVGAPassthrough>
> > >>  wiki page.
> > >>  
> > >> +=item B<gfx_passthru_primary=BOOLEAN>
> > >> +
> > >> +If set to true, indicates that one of the GPUs passed through to the
> > >> +domain is the primary one; therefore allows to the domain's stubdoman
> > >> +access permissions for the VGA framebuffer. Note that this option
> > >> +defaults to true.
> > >> +
> > > 
> > > Wouldn't it make sense to make it a pci <BDF> instead of boolean, 
> > > so that instead of: "one of the GPU's passed is the primary",
> > > you could actually specify: "this *specific* GPU passed through i would 
> > > like 
> > > to be the primary" ?
> > 
> > No. You can't just make some card primary (with "primary" really
> > meaning accessible via the legacy VGA interface). Within a host
> > there's exactly one card that can be primary. If that card gets
> > passed through, it can also be primary in the guest. Any other
> > card, not having the legacy VGA ports routed through the
> > corresponding circuitry, can't all of the sudden become the
> > primary one in a guest.
> > 
> > Consequently this shouldn't be a config file setting, but something
> > that gets worked out by looking at the PCI config spaces of the
> > passed through card and eventual upstream bridges.
> 
> What specifically should Arianna be looking for? THe PCI device class or
> something else?

Qemu-trad seems to use:
    if ( !gfx_passthru || real_device->pci_dev->device_class != 0x0300 )
        return ret;

Is that sufficient?



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