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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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