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

["Jan Beulich" <JBeulich@suse.com>]

>>> On 03.07.14 at 17:25, <Ian.Campbell@citrix.com> wrote:
> On Thu, 2014-07-03 at 16:17 +0100, Jan Beulich wrote:
>> >>> On 03.07.14 at 16:53, <Ian.Campbell@citrix.com> 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.

Jan