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 16:37 +0100, Jan Beulich wrote:
> >>> On 03.07.14 at 17:25, <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Thu, 2014-07-03 at 16:17 +0100, Jan Beulich wrote:
> >> >>> On 03.07.14 at 16:53, <Ian.Campbell@xxxxxxxxxx> wrote:
> >> > On Thu, 2014-07-03 at 15:50 +0100, Ian Campbell wrote:
> >> >> 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?
> >> 
> >> I don't think so - I'd expect secondary cards to also be showing this
> >> class/sub-class (but I have no system with two or more cards where
> >> I could at least empirically check), i.e. that would only be sufficient
> >> when there's no upstream bridge. PCI_BRIDGE_CTL_VGA (on
> >> upstream bridges) and maybe (but unlikely)
> >> PCI_COMMAND_VGA_PALETTE (on the device itself and perhaps also
> >> upstream bridges) would seem to be the indicators. But I'm afraid
> >> this really needs to be properly answered by a PCI expert.
> > 
> > Hrm, I'm not sure I see that happening any time soon...
> > 
> > Given that the above class-based check has apparently been fine since
> > however long could we live with it in the context of this series?
> 
> As said on an earlier version of the series - this is tools code, so
> ultimately you judge. I'm merely pointing out that we're apparently
> spreading a pre-existing shortcoming.

OK, IMHO given that it's totally orthogonal to the actual aim of the
series and given that it is not making things worse nor backing us into
a corner which we cannot get out we can live with it.

So we can go with the PCI device class based check.

Ian.



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