Re: [PATCH 04/17] gpu: nova-core: allocate PCI MSI vector during probe

[John Hubbard <jhubbard@nvidia.com>]

On 8/13/26 3:37 PM, Danilo Krummrich wrote:
> On Fri Aug 14, 2026 at 12:29 AM CEST, John Hubbard wrote:
>> On 8/13/26 3:26 PM, Danilo Krummrich wrote:
>>> On Thu Aug 13, 2026 at 11:43 PM CEST, John Hubbard wrote:
>>>> On 8/13/26 2:31 PM, Danilo Krummrich wrote:
>>>>> On Sat Aug 8, 2026 at 5:11 AM CEST, John Hubbard wrote:
>> ...
>>>>> I was about to ask if we really need to bother with MSI and shouln't just go for
>>>>> MSI-X only.
>>>>
>>>> I have an expensive, recent motherboard in my test machine, and it seems to only
>>>> expose MSI for my Turing, Ampere and Blackwell GPUs, in the non-SRIOV configuration.
>>>> So I'm thinking that MSI-X only would not work.
>>>
>>> Interesting, I just checked one of my Ada and one of my Ampere GPUs and neither
>>> reports MSI-X in the capabilities. Other devices show up with MSI-X though...
>>>
>>> Are we sure it's not an endpoint limitation? I really thought it's not.
>>
>> I haven't really dug into it, because it seems very clear that regardless
>> of the answer, we need to support both MSI and MSI-X in nova-core, right?
> 
> Apparently we do, and I'm a bit surprised by that. But it would still be
> interesting to know what's the constraint, as this seems to be an endpoint
> limitation. IOW, how can I exercise the MSI-X code?

I'm reasonably sure that it involves changing the BIOS settings, because that's
how I enabled the vGPU case about a year or so ago, when I was verifying that
this test machine could support the vGPU configuration. 

And I vaguely recall some Kconfig settings as well.

At some point, the machine started reporting lots of VFs, instead just the
PFs. But I don't remember what these each reported as far as MSI or MSI-X.


thanks,
-- 
John Hubbard